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LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 

Class 


LIBRARYxQF  cUSEEBL  STORIES 


A  SKIAGRAPH. 


THE 
STORY  OF  ELECTRICITY 


BY 

.      JOHN   MUNRO 

AUTHOR  OF  ELECTRICITY  AND  ITS  USES,  PIONEERS  OF  ELECTRICITYj 

HEROES  OF  THE  TELEGRAPH,  ETC.,  AND  JOINT  AUTHOR  OF 

MUNRO  AND  JAMIESON'S  POCKET-BOOK  OF 

ELECTRICAL  RULES  AND  TABLES 


THE 

UNIVERSITY 

OF 

WITH  ONS^JLT^A  TIONS 


NEW    YORK 

D.    APPLETON    AND    COMPANY 
1908 


COPYRIGHT,  1899,  1902, 
BY  D.  APPLETON  AND  COMPANY. 


PUBLISHERS'    NOTE. 


FOR  our  edition  of  this  work  the  terminolo- 
gy has  been  altered  to  conform  with  American 
usage,  some  new  matter  has  been  added,  and  a 
few  of  the  cuts  have  been  changed  and  some 
new  ones  introduced,  in  order  to  adapt  the  book 
fully  to  the  practical  requirements  of  American 
readers. 


193722 


CONTENTS. 


CHAPTER  PAGE 

I.  THE  ELECTRICITY  OF  FRICTION        ...  9 

II.  THE  ELECTRICITY  OF  CHEMISTRY     ...  26 

III.  THE  ELECTRICITY  OF  HEAT      ....  41 

IV.  THE  ELECTRICITY  OF  MAGNETISM     ...  45 
V.  ELECTROLYSIS 74 

VI.  THE  TELEGRAPH  AND  TELEPHONE    .        .        .81 
VII.  ELECTRIC  LIGHT  AND  HEAT      .        .        .        .no 

VIII.  ELECTRIC  POWER 124 

IX.  MINOR  USES  OF  ELECTRICITY    ....     143 
X.  THE  WIRELESS  TELEGRAPH        .        .        .        .174 

LIST  OF  BOOKS 179 

APPENDIX 181 

INDEX 189 

6 


LIST    OF    ILLUSTRATIONS. 


FIGURE 

A  Skiagraph  Frontispi 
i  —  A      Frictional      Ma- 
chine 

PAGE 

'ece 

II 
12 
13 
14 
17 
18 

19 
20 

22 

24 
28 
29 
30 
30 

33 
34 
35 

35 
37 
38 

40 
4i 

43 

FIGURE 

24  —  A    Thermo  -  electric 
Pile 
25  —  A  Natural  Magnet    . 
26     . 

PAGE 

44 
48 
50 
53 
54 
55 
56 
57 
58 

59 
60 
6r 

63 
64 
65 
66 
68 
70 
7i 
72 
78 
84 

87 

88 
89 

89 

3     

27 

28     

5     .        •        •                • 
6    

30  —  The  Galvanoscope    . 
31     

8  —  The  Electrophorus 
9  —  The  Leyden  Jar 
10  —  A     Wimshurst     Ma 
chine 
II—  A  Voltaic  Cell  . 

12      .            .           .            . 

13  —  Cells  in  Series  '. 
14  —  Cells  in  Parallel 
15—  A  Daniell  Cell  . 
1  6  —  The  Leclanche"  Cell  . 
17—  The  Bichromate  Cell 
18—  The  Chloride  of  Sil- 
ver Cell  . 
19—  The  E.G.  C.  Dry  Cell 
20  —  The  Voltameter 
21—  The    E.  P.  S.  Accu- 
mulator 
22  —  A     Thermo  -  electric 
Couple  . 
23  —  Thermo-electric  Cou- 
ples in  Series 

32    . 

v\ 

34     

35     •        -        .        .        . 
36  —  The  Induction  Coil  . 

VI     , 

38     , 

-2Q 

40  —  A  Dynamo 
41     
42     
43     
44     
45     •         •         .         •     '    • 
46  —  Morse  Signal  Alpha- 
bet        ... 
47  —  A      Simple      Electro 
Magnet  . 
48  —  Electro  Magnet 
49  —  The    Morse    Instru- 
ment 

LIST  OF  ILLUSTRATIONS. 


FIGURE' 

PAGE 

FIGURE                                                         PAGE 

50  —  The  Sounder    . 

9° 

75    .        .        .        .           124 

51  —  Sections  of  the  1894 

76    125 

Atlantic   Cable  — 

77  —  An  Electric  Railway    127 

Actual  Sizes  — 

78  —  An  Electric  Carnage  129 

Irish  Shore  End 

96 

79  —  An  Electric  Launch.  130 

Newfoundland 

80  —  An  Electric  Fan      .  131 

Shore  End 

97 

81  —  An  Electric  Sewing 

Deep  Sea  . 

97 

Machine       .         .132 

Light     Interme- 

82 —  An  Electric  Drill     .  133 

diate 

97 

83—  An   Electric   Trem- 

Heavy Interme- 

bling Bell    .    .     .  143 

diate 

97 

84  144 

52  —  The    Mirror    Instru- 

85    145 

ment 

98 

86  146 

53     

99 

87—  A  Magneto-Electric 

54  —  The  Siphon  Recorder 

100 

Bell      .         .         .147 

55     

101 

88  148 

56—  The  Telephone 

102 

89—  The  Electric  "But- 

57 —  The  Microphone 

104 

terfly"  Clock        .   151 

58     . 

1  06 

no  .                                            TC'> 

59    

1  08 

91  —  The  Photophone      .  153 

60    

III 

92  —  The  Induction  Bal- 

6 1  —  The  Pilsen  Lamp 

112 

ance     .         .         .155 

62  —  The  Brush  Lamp 

H3 

93  —  The  Electric  Pen    .   156 

63  —  The  Edison  Lamp    . 

"5 

94  —  The  Phonograph     .   159 

64     .         .         .         .         . 

116 

95  —  An      Electric     Gas 

65     

116 

Lighter         .         .160 

66    

118 

96  —  An    Electric    Lamp 

67     

118 

Lighter        .         .  162 

68     

119 

97  —  An  Electric  Fuse    .   163 

69  —  Electrical     Phospho- 

98    164 

rescence 

1  20 

99  165 

70—  The     Ideal     Illumi- 

100  —  Photographing    the 

nant 

121 

Unseen         .         .171 

71     .        .         .     •    . 

122 

101  —  Photographing     the 

12^ 

Skeleton       .         .  172 

*•*"  J 
123 

IO2  —  Marconi's    Appara- 

74     

123 

tus        ..,  177 

OF  THE 

UNIVERSITY 


THE   STORY  OF  ELECTRICITY. 


CHAPTER   I. 

THE    ELECTRICITY    OF    FRICTION. 

A  SCHOOLBOY  who  rubs  a  stick  of  sealing-wax 
on  the  sleeve  of  his  jacket,  then  holds  it  over 
dusty  shreds  or  bits  of  straw  to  see  them  fly  up 
and  cling  to  the  wax,  repeats  without  knowing 
it  the  fundamental  experiment  of  electricity.  In 
rubbing  the  wax  on  his  coat  he  has  electrified  it, 
and  the  dry  dust  or  bits  of  wool  are  attracted  to  it 
by  reason  of  a  mysterious  process  which  is  called 
"  induction." 

Electricity,  like  fire,  was  probably  discovered 
by  some  primeval  savage.  According  to  Hum- 
boldt,  the  Indians  of  the  Orinoco  sometimes 
amuse  themselves  by  rubbing  certain  beans  to 
make  them  attract  wisps  of  the  wild  cotton,  and 
the  custom  is  doubtless  very  old.  Certainly  the 
ancient  Greeks  knew  that  a  piece  of  amber  had 
when  rubbed  the  property  of  attracting  light 
bodies.  Thales  of  Miletus,  wisest  of  the  Seven 
Sages,  and  father  of  Greek  philosophy,  explained 
this  curious  effect  by  the  presence  of  a  "soul  "  in 
the  amber,  whatever  he  meant  by  that.  Thales 
flourished  600  years  before  the  Christian  era, 
while  Croesus  reigned  in  Lydia,  and  Cyrus  the 
Great,  in  Persia,  when  the  renowned  Solon  gave 
<-  9 


10  THE  STORY  OF   ELECTRICITY. 

his  laws  to  Athens,  and  Necos,  King  of  Egypt, 
made  war  on  Josiah,  King  of  Judah,  and  after  de- 
feating him  at  Megiddo,  dedicated  the  corslet  he 
had  worn  during  the  battle  to  Apollo  Didymaeus 
in  the  temple  of  Branchidae,  near  Miletus. 

Amber,  the  fossil  resin  of  a  pine  tree,  was 
found  in  Sicily,  the  shores  of  the  Baltic,  and 
other  parts  of  Europe.  It  was  a  precious  stone 
then  as  now,  and  an  article  of  trade  with  the 
Phoenicians,  those  early  merchants  of  the  Medi- 
terranean. The  attractive  power  might  enhance 
the  value  of  the  gem  in  the  eyes  of  the  supersti- 
tious ancients,  but  they  do  not  seem  to  have  in- 
vestigated it,  and  beyond  the  speculation  of 
Thales,  they  have  told  us  nothing  more  about  it. 

Towards  the  end  of  the  sixteenth  century  Dr. 
Gilbert  of  Colchester,  physician  to  Queen  Eliza- 
beth, made  this  property  the  subject  of  experi- 
ment, and  showed  that,  far  from  being  peculiar 
to  amber,  it  was  possessed  by  sulphur,  wax,  glass, 
and  many  other  bodies  which  he  called  electrics, 
from  the  Greek  word  elektron,  signifying  amber. 
This  great  Discovery  was  the  starting-point  of  the 
modern  science  of  electricity.  That  feeble  and 
mysterious  force  which  had  been  the  wonder  of 
the  simple  and  the  amusement  of  the  vain  could 
not  be  slighted  any  longer  as  a  curious  freak  of 
nature,  but  assuredly  none  dreamt  that  a  day  was 
dawning  in  which  it  would  transform  the  world. 

Otto  von  Guericke,  burgomaster  of  Magde- 
burg, was  the  first  to  invent  a  machine  for  excit- 
ing the  electric  power  in  larger  quantities  by 
simply  turning  a  ball  of  sulphur  between  the  bare 
hands.  Improved  by  Sir  Isaac  Newton  and  others, 
who  employed  glass  rubbed  with  silk,  it  created 
sparks  several  inches  long.  The  ordinary  fric- 


THE   ELECTRICITY  OF   FRICTION. 


II 


tional  machine  as  now  made  is  illustrated  in  fig- 
ure i,  where  P  is  a  disc  of  plate  glass  mounted 
on  a  spindle  and  turned  by  hand.  Rubbers  of 


FIG.  i.— A  Frictional  Machine. 

silk  R,  smeared  with  an  amalgam  of  mercury  and 
tin,  to  increase  their  efficiency,  press  the  rim  of 
the  plate  between  them  as  it  revolves,  and  a  brass 
conductor  C,  insulated  on  glass  posts,  is  fitted 
with  points  like  the  teeth  of  a  comb,  which,  as  the 
electrified  surface  of  the  plate  passes  by,  collect 
the  electricity  and  charge  the  conductor  with  posi- 
tive electricity.  Machines  of  this  sort  have  been 
made  with  plates  7  feet  in  diameter,  and  yielding 
sparks  nearly  2  feet  long. 

The  properties  of  the  "  electric  fire,"  as  it  was 
now  called,  were  chiefly  investigated  by  Dufay. 
To  refine  on  the  primitive  experiment  let  us  re- 
place the  shreds  by  a  pithball  hung  from  a  sup- 
port by  a  silk  thread,  as  in  figure  2.  If  we  rub 
the  glass  rod  vigorously  with  a  silk  handkerchief 
and  hold  it  near,  the  ball  will  fly  toward  the  rod. 


12 


THE   STORY  OF   ELECTRICITY. 


Similarly  we  may  rub  a  stick  of  sealing  wax,  a 
bar  of  sulphur,  indeed,  a  great  variety  of  sub- 
stances, and  by  this  easy  test  we  shall  find  them 
electrified.  Glass  rubbed  with  glass  will  not  show 
any  sign  of  electrification,  nor  will  wax  rubbed  on 
wax ;  but  when  the  rubber  is  of  a  different  mate- 
rial to  the  thing  rubbed,  we  shall  find,  on  using 
proper  precautions,  that  electrici- 
ty is  developed.  In  fact,  the 
property  which  was  once  thought 
peculiar  to  amber  is  found  to  be- 
long to  all  bodies.  Any  substance, 
when  rubbed  with  a  different  sub- 
stance^ becomes  electrified. 

The  electricity  thus 
produced  is  termed  fric- 
tional  electricity.  Of 
course  there  are  some 
materials,  such  as  am- 
ber, glass,  and  wax, 
which  display  the  ef- 
fect much  better  than 
others,  and  hence  its 
original  discovery. 
In  dry  frosty  weather  the  friction  of  a  tortoise- 
shell  comb  will  electrify  the  hair  and  make  it  cling 
to  the  teeth.  Sometimes  persons  emit  sparks  in 
pulling  off  their  flannels  or  silk  stockings.  The 
fur  of  a  cat,  or  even  of  a  garment,  stroked  in  the 
dark  with  a  warm  dry  hand  will  be  seen  to  glow, 
and  perhaps  heard  to  crackle.  During  winter  a 
person  can  electrify  himself  by  shuffling  in  his 
slippers  over  the  carpet,  and  light  the  gas  with  a 
spark  from  his  finger.  Glass  and  sealing-wax  are, 
however,  the  most  convenient  means  for  investi- 
gating the  electricity  of  friction. 


THE   ELECTRICITY   OF   FRICTION.  13 

A  glass  rod  when  rubbed  with  a  silk  handker- 
chief becomes,  as  we  have  seen,  highly  electric, 
and  will  attract  a  pithball  (fig.  2). 
Moreover,    if    we    substitute   the 
handkerchief   for   the  rod  it  will 
also  attract  the  ball  (fig.  3).  Clear- 
ly, then,  the  handkerchief  which 
rubbed   the   rod   as 
well  as  the  rod   it- 
self is  electrified.  At 
first  we  might  sup- 
pose that  the  hand- 
Fio.  3.  kerchief  had  merely 

rubbed  off  some  of 
the  electricity  from  the  rod,  but  a  lit- 
tle investigation  will  soon  show  that 
is  not  the  case.  If  we  allow  the  pith- 
ball  to  touch  the  glass  rod  it  will  steal  some  of 
the  electricity  on  the  rod,  and  we  shall  now  find 
the  ball  repelled  by  the  rod,  as  illustrated  in  figure 
4.  Then,  if  we  withdraw  the  rod  and  bring  for- 
ward the  handkerchief,  we  shall  find  the  ball  at- 
tracted by  it.  Evidently,  therefore,  the  electricity 
of  the  handkerchief  is  of  a  different  kind  from 
that  of  the  rod. 

Again,  if  we  allow  the  ball  to  touch  the  hand- 
kerchief and  rub  off  some  of  its  electricity,  the 
ball  will  be  repelled  by  the  handkerchief  and  at- 
tracted by  the  rod.  Thus  we  arrive  at  the  con- 
clusion that  whereas  the  glass  rod  is  charged  with 
one  kind  of  electricity,  the  handkerchief  which 
rubbed  it  is  charged  with  another  kind,  and,  judg- 
ing by  their  contrary  effects  on  the  charged  ball 
or  indicator,  they  are  "of  opposite  kinds.  To  dis- 
tinguish the  two  sorts,  one  is  called  positive  and 
the  other  negative  electricity. 


14  THE   STORY   OF   ELECTRICITY. 

Further   experiments   with    other   substances 
will    show  that    sometimes  the   rod   is   negative 
while  the  rubber  is  positive.     Thus,  if 
we  rub  the  glass  rod  with  cat's  fur 
instead  of  silk,  we  shall  find  the  glass 
negative  and  the  fur  positive.     Again, 
if  we  rub  a  stick  of  sealing-wax  with 
the   silk    handkerchief,  we  shall  find 
the  wax    negative    and  the  silk 
positive.     But  in  every  case  one 
is  the  opposite  of  the  other,  and 
moreover,  an  equal  quanti- 
ty of  both  sorts  of  electrici- 
ty is  developed,  one  kind  on 
the  rod  and  the  other  on  the 
rubber.    Hence  we  conclude 
that  equal  and  opposite  quan- 
IG*  *•  titles   of   electricity  are   sim- 

ultaneously developed  by  friction. 

If  any  two  of  the  following  materials  be 
rubbed  together,  that  higher  in  the  list  becomes 
positively  and  the  other  negatively  electrified : — 

POSITIVE  (  +  ). 
Cats'  fur. 
Polished  glass. 
Wool. 

Cork,  at  ordinary  temperature. 
Coarse  brown  paper. 
Cork,  heated. 
White  silk. 
Black  silk. 
Shellac. 
Rough  glass. 

NEGATIVE  (— ). 


THE   ELECTRICITY  OF   FRICTION.  15 

The  list  shows  that  quality,  as  well  as  kind, 
of  material  affects  the  production  of  electricity. 
Thus  polished  glass  when  rubbed  with  silk  is 
positive,  whereas  rough  glass  is  negative.  Cork 
at  ordinary  temperature  is  positive  when  rubbed 
with  hot  cork.  Black  silk  is  negative  to  white 
silk,  and  it  has  been  observed  that  the  best  radi- 
ator and  absorber  of  light  and  heat  is  the  most 
negative.  Black  cloth,  for  instance,  is  a  better 
radiator  than  white,  hence  in  the  Arctic  regions, 
where  the  body  is  much  warmer  than  the  sur- 
rounding air,  many  wild  animals  get  a  white  coat 
in  winter,  and  in  the  tropics,  where  the  sunshine 
is  hotter  than  the  body,  the  European  dons  a 
white  suit. 

The  experiments  of  figures  i,  2,  and  3  have 
also  shown  us  that  when  the  pithball  is  charged 
with  the  positive  electricity  of  the  glass  rod  it  is 
repelled  by  the  like '  charge  upon  the  rod,  and 
.  attracted  by  the  negative  or  unlike  charge  on  the 
handkerchief.  Again,  when  it  is  charged  with 
the  negative  electricity  of  the  handkerchief  it  is 
repelled  by  the  like  charge  on  the  handkerchief 
and  attracted  by  the  positive  or  unlike  charge  on 
the  rod.  Therefore  it  is  usual  to  say  that  like 
electricities  repel  and  tmlike  electricities  attract  each 
other. 

We  have  said  that  all  bodies  yield  electricity 
under  the  friction  of  dissimilar  bodies;  but  this 
cannot  be  proved  for  every  body  by  simply  hold- 
ing it  in  one  hand  and  rubbing  it  with  the  excitor, 
as  may  be  done  in  the  case  of  glass.  For  instance, 
if  we  take  a  brass  rod  in  the  hand  and  apply  the 
rubber  vigorously,  it  will  fail  to  attract  the  pith- 
ball,  for  there  is  no  trace  of  electricity  upon  it. 
This  is  because  the  metal  differs  from  the  glass 


16  THE  STORY  OF  ELECTRICITY. 

in  another  electrical  property,  and  they  must 
therefore  be  differently  treated.  Brass,  in  fact, 
is  a  conductor  of  electricity  and  glass  is  not.  In 
other  words,  electricity  is  conducted  or  led  away 
by  brass,  so  that,  as  soon  as  it  is  generated  by  the 
friction,  it  flows  through  the  hand  and  body  of 
the  experimenter,  which  are  also  conductors,  and 
is  lost  in  the  ground.  Glass  on  the  other  hand, 
is  an  insulator,  and  the  electricity  remains  on  the 
surface  of  it.  If,  however,  we  attach  a  glass 
handle  to  the  rod  and  hold  it  by  that  whilst  rub- 
bing it,  the  electricity  cannot  then  escape  to  the 
earth,  and  the  brass  rod  will  attract  the  pith-ball. 
All  bodies  are  conductors  of  electricity  in 
some  degree,  but  they  vary  so  enormously  in 
this  respect  that  it  has  been  found  convenient 
to  divide  them  into  two  extreme  classes — con- 
ductors and  insulators.  These  run  into  each 
other  through  an  intermediate  group,  which  are 
neither  good  conductors  nor  good  insulators. 
The  following  are  the  chief  examples  of  these 
classes : — 

CONDUCTORS. — All  the  metals,  carbon. 

INTERMEDIATE  (bad  conductors  and  bad  in- 
sulators).— Water,  aqueous  solutions,  moist 
bodies ;  wood,  cotton,  hemp,  and  paper  in 
any  but  a  dry  atmosphere ;  liquid  acids, 
rarefied  gases. 

INSULATORS. — Paraffin  (solid  or  liquid),  ozo- 
kerit,  turpentine,  silk,  resin,  sealing-wax  or 
shellac,  indiarubber,  gutta  percha,  ebonite, 
ivory,  dry  wood,  dry  glass  or  porcelain, 
mica,  ice,  air  at  ordinary  pressures. 

It  is  remarkable  that  the  best  conductors  of 
electricity,  that  is  to  say,  the  substances  which 


THE   ELECTRICITY  OF   FRICTION. 


offer  least  resistance  to  its  passage,  for  instance  the 
metals,  are  also  the  best  conductors  of  heat,  and 
that  insulators  made  red  hot  become  conductors. 
Air  is  an  excellent  insulator,  and  hence  we  are 

able     to    perform 
-.^  our      experiments 

Sv*--».  on  frictional  elec- 
..•'•  |  tricity  in  it.  We 
I  can  also  run  bare 
telegraph  wires 
by  taking  care  to  insulate 
glass  or  porcelain  from  the 
poles  which  support  them 
ground.  Water,  on  the  other 
partial  conductor,  and  a  great 
the  storage  or  conveyance  of 
from  its  habit  of  soaking  in- 
metals,  or  depositing  in  a 
on  the  cold  surfaces  of  insu- 
as  glass,  porcelain,  or  ebon- 
remedy  is  to  exclude  it,  or 
insulators  warm  and  dry,  or 
with  shellac  varnish,  wax,  or 


through  it, 
them  with 
wo  o  d  e  n 
above  the 
hand,  is  a 
enemy  to 
electricity, 
to  porous 
film  of  dew 
lators  such 
ite.  '  The 
keep  the 
coat  them 


FIG.  5. 


paraffin.  Submarine  telegraph  wires  running  un- 
der the  sea  are  usually  insulated  from  the  sur- 
rounding water  by  india-rubber  or  gutta  percha. 

The  distinction  between  conductors  and  non- 
conductors or  insulators  was  first  observed  by 
Stephen  Gray,  a  pensioner  of  the  Charter-house. 
Gray  actually  transmitted  a  charge  of  electricity 
along  a  pack-thread  insulated  with  silk,  to  a  dis- 
tance of  several  hundred  yards,  and  thus  took 
an  important  step  in  the  direction  of  the  electric 
telegraph. 

It  has  since  been  found  ft&A.  frictional  electrici- 
ty appears  only  on  the  external  surface  of  conductors. 


i8 


THE  STORY   OF   ELECTRICITY. 


This  is  well  shown  by  a  device  of  Faraday 
resembling  a  small  butterfly  net  insulated  by  a 
glass  handle  (fig.  5).  If  the  net  be  charged  it  is 
found  that  the  electrification  is  only  outside,  and 
if  it  be  suddenly  drawn  outside  in,  as  shown  by 
the  dotted  line,  the  electrification  is  still  found 
outside,  proving  that  the  charge  has  shifted  from 
the  inner  to  the  outer  surface.  In  the  same  way 
if  a  hollow  conductor  is  charged  with  electricity, 
none  is  discoverable  in  the  interior.  Moreover, 
its  distribution  on  the  exterior  is  influenced  by  the 
shape  of  the  outer  surface.  On  a  sphere  or  ball 
it  is  evenly  distributed  all  round,  but  it  accu- 
mulates on  sharp  edges  or  corners,  and  most  of 
all  on  points,  from  which  it  is  easily  discharged. 

A  neutral  body  can,  as  we  have  seen  (fig.  4), 
be  charged  by  contact  with  an  electrified  body ; 
but  it  can  also  be  charged 
by  induction,  or  the  influence 
of  the  electrified  body  at  a 
distance. 

Thus  if  we  electrify  a 
glass  rod  positively  ( + )  and 
bring  it  near  a  neutral  or 
unelectrified  brass  ball,  in- 
sulated on  a  glass  support, 
as  in  figure  6,  we  shall  find 
the  side  of  the  ball  next  the 
rod  no  longer  neutral  but 
negatively  electrified  (—), 
and  the  side  away  from 
the  rod  positively  elec- 
trified (  +  ). 

If  we  take  away  the  rod  again  the  ball  will 
return  to  its  neutral  or  non-electric  state,  show- 
ing that  the  charge  was  temporarily  induced  by 


FIG.  6. 


THE  ELECTRICITY  OF   FRICTION. 


the  presence  of  the  electrified  rod.  Again,  if,  as 
in  figure  7,  we  have  two  insulated  balls  touching 
each  other,  and  bring  the  rod  up,  that  nearest 
the  rod  will  become  negative  and  that  farthest 
from  it  positive.  It  appears  from  these  facts 
that  electricity  has 
the  power  of  disturb- 
ing or  decomposing 
the  neutral  state  of  a 
neighbouring  conduct- 
or, and  attracting  the 
unlike  while  it  re- 
pels the  like  induced 
charge.  Hence,  too, 
it  is  that  the  electri- 
fied amber  or  sealing- 
wax  is  able  to  attract 
a  light  straw  or  pith- 
ball.  The  effect  sup- 
plies a  simple  way  of 
developing  a  large 
amount  of  electricity  from  a  small  initial  charge. 
For  if  in  figure  6  the  positive  side  of  the  ball  be 
connected  for  a  moment  to  earth  by  a  conductor, 
its  positive  charge  will  escape,  leaving  the  nega- 
tive on  the  ball,  and  as  there  is  no  longer  an 
equal  positive  charge  to  recombine  with  it  when 
the  exciting  rod  is  withdrawn,  it  remains  as  a 
negative  charge  on  the  ball.  Similarly,  if  we 
separate  the  two  balls  in  figure  7,  we  gain  two 
equal  charges — one  positive,  the  other  negative. 
These  processes  have  only  to  be  repeated  by  a 
machine  in  order  to  develop  very  strong  charges 
from  a  feeble  source. 

Faraday  saw  that  the  intervening  air  played  a 
part  in  this  action  at  a  distance,  and  proved  con- 


FIG.  7. 


20 


THE  STORY  OF  ELECTRICITY. 


clusively  that  the  value  of  the  induction  depended 
on  the  nature  of  the  medium  between  the  induced 
and  the  inducing  charge.  He  showed,  for  exam- 
ple, that  the  induction  through  an  intervening 
cake  of  sulphur  is  greater  than  through  an  equal 
thickness  of  air.  This  property  of  the  medium  is 
termed  its  inductive  capacity. 

The  Electrophorus,  or  carrier  of  electricity,  is 
a  simple  device  for  developing  and  conveying  a 
charge  on  the  principle  of  induction.  It  consists, 


FlG.  8. — The  Electrophorus. 

as  shown  in  figure  8,  of  a  metal  plate  B  having 
an  insulating  handle  of  glass  H,  and  a  flat  cake 
of  resin  or  ebonite  R.  If  the  resin  is  laid  on  a 
table  and  briskly  rubbed  with  cat's  fur  it  becomes 
negatively  electrified.  The  brass  plate  is  then 
lifted  by  the  handle  and  laid  upon  the  cake.  It 
touches  the  electrified  surface  at  a  few  points, 
and  takes  a  minute  charge  from  these  by  contact. 


THE   ELECTRICITY  OF   FRICTION.  21 

The  rest  of  it,  however,  is  insulated  from  the 
resin  by  the  air.  In  the  main,  therefore,  the 
negative  charge  of  the  resin  is  free  to  induce  an 
opposite  or  positive  charge  on  the  lower  surface 
and  a  negative  charge  on  the  upper  surface  of 
the  plate.  By  touching  this  upper  surface  with 
the  ringer,  as  shown  in  figure  8,  the  negative 
charge  will  escape  through  the  body  to  the 
ground  or  "  earth,"  as  it  is  technically  called, 
and  the  positive  charge  will  remain  on  the  plate. 
We  can  withdraw  it  by  lifting  the  plate,  and 
prove  its  existence  by  drawing  a  spark  from  it 
with  the  knuckle.  The  process  can  be  repeated 
as  long  as  the  negative  charge  continues  on  the 
resin. 

These  tiny  sparks  from  the  electrophorus,  or 
the  bigger  discharges  of  an  electrical  machine, 
can  be  stored  in  a  simple  apparatus  called  a 
Leyden  jar,  which  was  discovered  by  accident. 
One  day  Cuneus,  a  pupil  of  Muschenbroeck,  pro- 
fessor in  the  University  of  Leyden,  was  trying 
to  charge  some  water  in  a  glass  bottle  by  con- 
necting it  with  a  chain  to  the  sparkling  knob  of 
an  electrical  machine.  Holding  the  bottle  in  one 
hand,  he  undid  the  chain  with  the  other,  and 
received  a  violent  shock  which  cast  the  bottle  on 
the  floor.  Muschenbroeck,  eager  to  verify  the 
phenomenon,  repeated  the  experiment,  with  a 
still  more  lively  and  convincing  result.  His 
nerves  were  shaken  for  two  days,  and  he  after- 
wards protested  that  he  would  not  suffer  another 
shock  for  the  whole  kingdom  of  France. 

The  Leyden  jar  is  illustrated  in  figure  9,  and 
consists  in  general  of  a  glass  bottle  partly  coated 
inside  and  out  with  tinfoil  F,  and  having  a  brass 
knob  K  connecting  with  its  internal  coat.  When 


22 


THE   STORY   OF   ELECTRICITY. 


the  charged  plate  or  conductor  of  the  electro- 
phorus  touches  the  knob  the  inner  foil  takes  a 
positive  charge,  which  induces  a  negative  charge 


FIG.  9.— The  Leyden  Jar. 


in  the  outer  foil  through  the  glass.  The  corre- 
sponding positive  charge  induced  at  the  same 
time  escapes  through  the  hand  to  the  ground  or 
"earth."  The  inner  coating  is  now  positively 
and  the  outer  coating  negatively  electrified,  and 
these  two  opposite  charges  bind  or  hold  each 
other  by  mutual  attraction.  The  bottle  will 
therefore  continue  charged  for  a  long  time;  in 
short,  until  it  is  purposely  discharged  or  the  two 
electricities  combine  by  leakage  over  the  surface 
of  the  glass. 

To  discharge  the  jar  we  need  only  connect  the 
two  foils  by  a  conductor,  and  thus  allow  the 
separated  charges  to  combine.  This  should  be 
done  by  joining  the  outer  to  the  inner  coat  with  a 
stout  wire,  or,  better  still,  the  discharging  tongs 
T,  as  shown  in  the  figure.  Otherwise,  if  the 


THE   ELECTRICITY   OF   FRICTION.  23 

tongs  are  first  applied  to  the  inner  coat,  the 
operator  twill  receive  the  charge  through  his 
arms  and  chest  in  the  manner  of  Cuneus  and 
Muschenbroeck. 

Leyden  jars  can  be  connected  together  in 
"batteries,"  so  as  to  give  very  powerful  effects. 
One  method  is  to  join  the  inner  coat  of  one  to 
the  outer  coat  of  the  next.  This  is  known  as 
connecting  in  "  series,"  and  gives  a  very  long 
spark.  Another  method  is  to  join  the  inner  coat 
of  one  to  the  inner  coat  of  the  next,  and  similarly 
all  the  outer  coats  together.  This  is  called  con- 
necting "  in  parallel,"  or  quantity,  and  gives  a 
big,  but  not  a  long  spark. 

Of  late  years  the  principle  of  induction,  which 
is  the  secret  of  the  Leyden  jar- and  electrophorus, 
has  been  applied  in  constructing  "  influence " 
machines  for  generating  electricity.  Perhaps  the 
most  effective  of  these  is  the  Wimshurst,  which 
we  illustrate  in  figure  10,  where  PP  are  two 
circular  glass  plates  which  rotate  in  opposite 
directions  on  turning  the  handle.  On  the  outer 
rim  of  each  is  cemented  a  row  of  radial  slips  of 
metal  at  equal  intervals.  The  slips  at  opposite 
ends  of  a  diameter  are  connected  together  twice 
during  each  revolution  of  the  plates  by  wire 
brushes  S,  and  collecting  combs  TT  serve  to 
charge  the  positive  and  negative  conductors  CC, 
which  yield  very  powerful  sparks  at  the  knobs 
K  above.  The  given  theory  of  this  machine  may 
be  open  to  question,  but  there  can  be  no  doubt 
of  its  wonderful  performance.  A  small  one  pro- 
duces a  violent  spark  8  or  10  inches  long  after  a 
few  turns  of  the  handle. 

The  electricity  of  friction  is  so  unmanageable 
that  it  has  not  been  applied  in  practice  to  any 


24  THE   STORY   OF   ELECTRICITY. 

great  extent.  In  1753  Mr.  Charles  Morrison,  of 
Greenock,  published  the  first  plan  of  an  electric 
telegraph  in  the  Scots  Magazine,  and  proposed  to 
charge  an  insulated  wire  at  the  near  end  so  as  to 


FIG.  10. — A  Wimshurst  Machine. 

make  it  attract  printed  letters  of  the  alphabet  at 
the  far  end.  Sir  Francis  Ronalds  also  invented  a 
telegraph  actuated  by  this  kind  of  electricity,  but 
neither  of  these  came  into  use.  Morrison,  an 
obscure  genius,  was  before  his  age,  and  Ronalds 
was  politely  informed  by  the  Government  of  his 


THE  ELECTRICITY  OF  FRICTION.  25 

day  that  "  telegraphs  of  any  kind  were  wholly 
unnecessary."  Little  instruments  for  lighting  gas 
by  means  of  the  spark  are,  however,  made,  and 
the  noxious  fumes  of  chemical  and  lead  works 
are  condensed  and  laid  by  the  discharge  from  the 
Wimshurst  machine.  The  electricity  shed  in  the 
air  causes  the  dust  and  smoke  to  adhere  by  in- 
duction and  settle  in  flakes  upon  the  sides  of 
the  flues.  Perhaps  the  old  remark  that  "  smuts  " 
or  "  blacks"  falling  to  the  ground  on  a  sultry  day 
are  a  sign  of  thunder  is  traceable  to  a  similar 
action. 

The  most  important  practical  result  of  the 
early  experiments  with  frictional  electricity  was 
Benjamin  Franklin's  great  discovery  of  the  iden- 
tity of  lightning  and  the  electric  spark.  One 
day  in  June,  1792,  he  went  to  the  common  at 
Philadelphia  and  flew  a  kite  beneath  a  thunder- 
cloud, taking  care  to  insulate  his  body  from  the 
cord.  After  a  shower  had  wetted  the  string  and 
made  it  a  conductor,  he  was  able  to  draw  sparks 
from  it  with  a  key  and  to  charge  a  Leyden  jar. 
The  man  who  had  u  robbed  Jupiter  of  his  thun- 
derbolts "  became  celebrated  throughout  the 
world,  and  lightning  rods  or  conductors  for  the 
protection  of  life  and  property  were  soon  brought 
out.  These,  in  their  simplest  form,  are  tapes  or 
stranded  wires  of  iron  or  copper  attached  to  the 
walls  of  the  building.  The  lower  end  of  the  con- 
ductor is  soldered  to  a  copper  plate  buried  in  the 
moist  subsoil,  or,  if  the  ground  is  rather  dry,  in  a 
pit  containing  coke.  Sometimes  it  is  merely  sol- 
dered to  the  water  mains  of  the  house.  The 
upper  end  rises  above  the  highest  chimney,  tur- 
ret, or  spire  of  the  edifice,  and  branches  into 
points  tipped  with  incorrosive  metal,  such  as 


26  THE  STORY   OF  ELECTRICITY. 

platinum.  It  is  usual  to  connect  all  the  outside 
metal  of  the  house,  such  as  the  gutters  and  finials 
to  the  rod  by  means  of  soldered  joints,  so  as  to 
form  one  continuous  metallic  network  or  artery 
for  the  discharge. 

When  a  thundercloud  charged  with  electricity 
passes  over  the  ground,  it  induces  a  charge  of  an 
opposite  kind  upon  it.  The  cloud  and  earth  with 
air  between  are  analogous  to  the  charged  foils  of 
the  Leyden  jar  separated  by  the  glass.  The  two 
electricities  of  the  jar,  we  know,  attract  each 
other,  and  if  the  insulating  glass  is  too  weak 
to  hold  them  asunder,  the  spark  will  pierce  it. 
Similarly,  if  the  insulating  air  cannot  resist  the 
attraction  between  the  thundercloud  and  the 
earth,  it  will  be  ruptured  by  a  flash  of  lightning. 
The  metal  rod,  however,  tends  to  allow  the  two 
charges  of  the  cloud  and  earth  to  combine  quietly 
or  to  shunt  the  discharge  past  the  house. 


CHAPTER   II. 

THE    ELECTRICITY    OF    CHEMISTRY. 

A  MORE  tractable  kind  of  electricity  than  that 
of  friction  was  discovered  at  the  beginning  of 
the  present  century.  The  story  goes  that  some 
edible  frogs  were  skinned  to  make  a  soup  for 
Madame  Galvani,  wife  of  the  professor  of  anatomy 
in  the  University  of  Bologna,  who  was  in  delicate 
health.  As  the  frogs  were  lying  in  the  laboratory 
of  the  professor  they  were  observed  to  twitch 
each  time  a  spark  was  drawn  from  an  electrical 
machine  that  stood  by.  A  similar  twitching  was 


THE   ELECTRICITY   OF   CHEMISTRY.  27 

also  noticed  when  the  limbs  were  hung  by  copper 
skewers  from  an  iron  rail.  Galvani  thought  the 
spasms  were  due  to  electricity  in  the  animal,  and 
produced  them  at  will  by  touching  the  nerve  of  a 
limb  with  a  rod  of  zinc,  and  the  muscle  with  a 
rod  of  copper  in  contact  with  the  zinc.  It  was 
proved,  however,  by  Alessandra  Volta,  professor 
of  physics  in  the  University  of  Pavia,  that  the 
electricity  was  not  in  the  animal,  but  generated 
by  the  contact  of  the  two  dissimilar  metals  and 
the  moisture  of  the  flesh.  Going  a  step  further, 
in  the  year  1800  he  invented  a  new  source  of 
electricity  on  this  principle,  which  is  known  as 
"  Volta's  pile."  It  consists  of  plates  or  discs  of 
zinc  and  copper  separated  by  a  wafer  of  cloth 
moistened  with  acidulated  water.  When  the  zinc 
and  copper  are  joined  externally  by  a  wire,  a 
current  of  electricity  is  found  in  the  wire.  One 
pair  of  plates  with  the  liquid  between  makes  a 
"  couple  "  or  element ;  and  two  or  more,  built  one 
above  another  in  the  same  order  of  zinc,  copper, 
zinc,  copper,  make  the  pile.  The  extreme  zinc 
and  copper  plates,  when  joined  by  a  wire,  are 
found  to  deliver  a  current. 

This  form  of  the  voltaic,  or,  as  it  is  sometimes 
called,  galvanic  battery,  has  given  place  to  the 
"cell"  shown  in  figure  n,  where  the  two  plates 
Z  C  are  immersed  in  acidulated  water  within  the 
vessel,  and  connected  outside  by  the  wire  W. 
The  zinc  plate  has  a  positive  and  the  copper  a 
negative  charge.  The  positive  current  flows  from 
the  zinc  to  the  copper  inside  the  cell  and  from  the 
copper  to  the  zinc  outside  the  cell,  as  shown  by 
the  arrows.  It  thus  makes  a  complete  round, 
which  is  called  the  voltaic  "  circuit,"  and  if  the 
circuit  is  broken  anywhere  it  will  not  flow  at  all. 


28 


THE   STORY   OF   ELECTRICITY. 


FIG.  ii. 
A  Voltaic  Cell. 


The  positive  electricity  of  the  zinc  appears  to  trav- 
erse the  liquid  to  the  copper,  from  which  it  flows 
through  the  wire  to  the  zinc. 
The  effect  is  that  the  end  of  the 
wire  attached  to  the  copper  is 
positive  (  +  ),  and  called  the 
positive  "  pole "  or  electrode, 
while  the  end  attached  to  the 
zinc  is  negative  (— ),  and  called 
the  negative  pole  or  electrode. 
"  A  simple  and  easy  way  to 
avoid  confusion  as  to  the  direc- 
tion of  the  current,  is  to  remem- 
ber that  the  positive  current  flows 
from  the  copper  to  the  zinc  at  the 
point  of  metallic  contact." 
The  generation  of  this  current  is  accompanied 
by  chemical  action  in  the  cell.  Experiment  shows 
that  the  mere  contact  of  dissimilar  materials,  such 
as  copper  and  zinc,  electrifies  them — zinc  being 
positive  and  copper  negative ;  but  contact  alone 
does  not  yield  a  continuous  current  of  electricity. 
When  we  plunge  the  two  metals,  still  in  contact, 
either  directly  or  through  a  wire,  into  water  pref- 
erably acidulated,  a  chemical  action  is  set  up,  the 
water  is  decomposed,  and  the  zinc  is  consumed. 
Water,  as  is  well  known,  consists  of  oxygen  and 
hydrogen.  The  oxygen  combines  with  the  zinc 
to  form  oxide  of  zinc,  and  the  hydrogen  is  set  free 
as  gas  at  the  surface  of  the  copper  plate.  So 
long  as  this  process  goes  on,  that  is  to  say,  as 
long  as  there  is  zinc  and  water  left,  we  get  an 
electric  current  in  the  circuit.  The  existence  of 
such  a  current  may  be  proved  by  a  very  simple 
experiment.  Place  a  penny  above  and  a  dime  be- 
low the  tip  of  the  tongue,  then  bring  their  edges 


THE   ELECTRICITY  OF  CHEMISTRY. 


29 


into  contact,  and  you  will  feel  an  acid  taste  in  the 
mouth. 

Figure   12   illustrates  the   supposed  chemical 
action   in    the   cell.      On  the  left  hand   are  the 


o 

o 

bo 


FIG.  12. 


zinc  and  copper  plates  (Z  C)  disconnected  in  the 
liquid.  The  atoms  of  zinc  are  shown  by  small 
circles;  the  molecules  of  water,  that  is,  oxygen, 
and  hydrogen  (H2  O)  by  lozenges  of  unequal  size. 
On  the  right  hand  the  plates  are  connected  by  a 
wire  outside  the  cell ;  the  current  starts,  and  the 
chemical  action  begins.  An  atom  of  zinc  unites 
with  an  atom  of  oxygen,  leaving  two  atoms  of 
hydrogen  thus  set  free  to  combine  with  another 
atom  of  oxygen,  which  in  turn  frees  two  atoms  of 
hydrogen.  This  interchange  of  atoms  goes  on 
until  the  two  atoms  of  hydrogen  which  are  freed 
last  abide  on  the  surface  of  the  copper.  The 
"  contact  electricity  "  of  the  zinc  and  copper  prob- 
ably begins  the  process,  and  the  chemical  action 
keeps  it  up.  Oxygen,  being  an  "  electro-negative  " 
element  in  chemistry,  is  attracted  to  the  zinc,  and 
hydrogen,  being  "  electro-positive,"  is  attracted 
to  the  copper. 

The  difference  of  electrical  condition  or  "  po- 
tential "  between  the  plates  by  which  the  current 
is  started  has  been  called  the  electromotive  force,  or 
force  which  puts  the  electricity  in  motion.  The 


30  THE  STORY  OF   ELECTRICITY. 

obstruction  or  hindrance  which  the  electricity 
overcomes  in  passing  through  its  conductor  is 
known  as  the  resistance.  Obviously  the  higher 
the  electromotive  force  and  the  lower  the  resist- 
ance, the  stronger  will  be  the  current  in  the  con- 
ductor. Hence  it  is  desirable  to  have  a  cell  which 
will  give  a  high  electromotive  force  and  a  low  in- 
ternal resistance. 

Voltaic  cells  are  grouped  together  in  the  mode 
of  Leyden  jars.     Figure  13  shows  how  they  are 


FIG.  13.— Cells  in  Series. 


joined  "in  series/'  the  zinc  or  negative  pole  of 
one  being  connected  by  wire  to  the  copper  or 
positive  pole  of  the  next.  This  arrangement  mul- 


FiG.  14.— Cells  in  Parallel. 

tiplies  alike  the  electromotive  force  and  the  re- 
sistance. The  electromotive  force  of  the  battery 
is  the  sum  of  the  electromotive  forces  of  all  the 


THE   ELECTRICITY  OP  CHEMISTRY.  31 

cells,  and  the  resistance  of  the  battery  is  the  sum 
of  the  resistances  of  all  the  cells.  High  electro- 
motive forces  or  "  pressures "  capable  of  over- 
coming high  resistances  outside  the  battery  can 
be  obtained  in  this  way. 

Figure  14  shows  how  the  zincs  are  joined  "  in 
parallel,"  the  zinc  or  negative  pole  of  one  being 
connected  by  wire  to  the  zinc  or  negative  pole  of 
the  rest,  and  all  the  copper  or  positive  poles  to- 
gether. This  arrangement  does  not  increase  the 
electromotive  force,  but  diminishes  the  resistance. 
In  fact,  the  battery  is  equivalent  to  a  single  cell 
having  plates  equal  in  area  to  the  total  area  of  all 
the  plates.  Although  unable  to  overcome  a  high 
resistance,  it  can  produce  a  large  volume  or  quan- 
tity of  electricity. 

Numerous  voltaic  combinations  and  varieties 
of  cell  have  been  found  out.  In  general,  where- 
ever  two  metals  in  contact  are  placed  in  a  liquid 
which  acts  with  more  chemical  energy  on  one 
than  on  the  other,  as  sulphuric  acid  does  on 
zinc  in  preference  to  copper,  there  is  a  develop- 
ment of  electricity.  Readers  may  have  seen  how 
an  iron  fence  post  corrodes  at  its  junction  with 
the  lead  that  fixes  it  in  the  stone.  This  decay  is 
owing  to  the  wet  forming  a  voltaic  couple  with 
the  two  dissimilar  metals  and  rusting  the  iron. 
In  the  following  list  of  materials,  when  any  two 
in  contact  are  plunged  in  dilute  acid,  that  which 
is  higher  in  the  order  becomes  the  positive  plate 
or  negative  pole  to  that  which  is  lower: — 
POSITIVE.  Iron.  Silver. 

Zinc.  Nickel.  Gold. 

Cadmium.  Bismuth.  Platinum. 

Tin.  Antimony.  Graphite. 

Lead.  Copper.  NEGATIVE. 


32  THE  STORY  OF  ELECTRICITY. 

There  being  no  chemical  union  between  the 
hydrogen  and  copper  in  the  zinc  and  copper 
couple,  that  gas  accumulates  on  the  surface  of 
the  copper  plate,  or  is  liberated  in  bubbles.  Now, 
hydrogen  is  positive  compared  with  copper,  hence 
they  tend  to  oppose  each  other  in  the  combina- 
tion. The  hydrogen  diminishes  the  value  of  the 
copper,  the  current  grows  weaker,  and  the  cell  is 
said  to  u  polarise."  It  follows  that  a  simple  water 
cell  is  not  a  good  arrangement  for  the  supply  of  a 
steady  current. 

The  Daniell  cell  is  one  of  the  best,  and  gives  a 
very  constant  current.  In  this  battery  the  copper 
plate  is  surrounded  by  a  solution  of  sulphate  of 
copper  (Cu  SO±),  which  the  hydrogen  decomposes, 
forming  sulphuric  acid  (H2SO^),  thus  taking  itself 
out  of  the  way,  and  leaving  pure  copper  (Cu)  to 
be  deposited  as  a  fresh  surface  on  the  copper 
plate.  A  further  improvement  is  made  in  the 
cell  by  surrounding  the  zinc  plate  with  a  solution 
of  sulphate  of  zinc  (Zn  SO±),  which  is  a  good  con- 
ductor. Now,  when  the  oxide  of  zinc  is  formed 
by  the  oxygen  uniting  with  the  zinc,  the  free  sul- 
phuric acid  combines  with  it,  forming  more  sul- 
phate of  zinc,  and  maintaining  the  conductivity  of 
the  cell.  It  is  only  necessary  to  keep  up  the  sup- 
ply of  zinc,  water,  and  sulphate  of  copper  to  pro- 
cure a  steady  current  of  electricity. 

The  Daniell  cell  is  constructed  in  various 
ways.  In  the  earlier  models  the  two  plates 
with  their  solutions  were  separated  by  a  porous 
jar  or  partition,  which  allowed  the  solutions  to 
meet  without  mixing,  and  the  current  to  pass. 
Sawdust  moistened  with  the  solutions  is  some- 
times used  for  this  porous  separator,  for  instance, 
on  board  ships  for  laying  submarine  cables, 


OF 


ICTRICITY   OF   CHEMISTRY. 


33 


where  the  rolling  of  the  waves  would  blend  the 
liquids. 

In  the  "  gravity  "  Daniell  the  solutions  are 
kept  apart  by  their  specific  gravities,  yet  mingle 
by  slow  diffusion.  Figure  15  illustrates  this  com- 
mon type  of  cell,  where 
Z  is  the  zinc  plate  in  a 
solution  of  sulphate  of 
zinc,  and  C  is  the  copper 
plate  in  a  solution  of  sul- 
phate of  copper,  fed  by 
crystals  of  the  "  blue  vit- 
riol." The  wires  to  con- 
nect the  plates  are  shown 
at  WW.  It  should  be  no- 
ticed that  the  zinc  is  cast 
like  a  wheel  to  expose  a 
larger  surface  to  oxida- 
tion, and  to  reduce  the 
resistance  of  the  cell, 
thus  increasing  the  yield 
of  current.  The  extent 
of  surface  is  not  so  important  in  the  case  of  the 
copper  plate,  which  is  not  acted  on,  and  in  this  case 
is  merely  a  spiral  of  wire,  helping  to  keep  the  solu- 
tions apart  and  the  crystals  down.  The  Daniell 
cell  is  much  employed  in  telegraphy.  The  Bunsen 
cell  consists  of  a  zinc  plate  in  sulphuric  acid,  and  a 
carbon  plate  in  nitric  acid,  with  a  porous  separator 
between  the  liquids.  During  the  action  of  the  cell, 
hydrogen,  which  is  liberated  at  the  carbon  plate, 
is  removed  by  combining  with  the  nitric  acid. 
The  Grove  cell  is  a  modification  of  the  Bunsen, 
with  platinum  instead  of  carbon.  The  Smee  cell 
is  a  zinc  plate  side  by  side  with  a  "platinised  " 
silver  plate  in  dilute  sulphuric  acid.  The  silver 


FIG.  15.— A  Daniell  Cell. 


34 


THE   STORY   OF   ELECTRICITY. 


is  coated  with  rough  platinum  to  increase  the  sur- 
face and  help  to  dislodge  the  hydrogen  as  bub- 
bles and  keep  it  from  polarising  the  cell.  The 
Bunsen,  Grove,  and  Smee  batteries  are,  however, 
more  used  in  the  laboratory  than  elsewhere. 

The  Leclanche  is  a  fairly  constant  cell,  which 
requires  little  attention.  It  "  polarises  "  in  action 
but  soon  regains  its  normal  strength  when  allowed 
to  rest,  and  hence  it  is  useful  for  working  electric 
bells  and  telephones.  As  shown  in  figure  16,  it 
consists  of  a  zinc  rod  with  its  connecting  wire  Z, 
and  a  carbon  plate  C  with  its  binding  screw,  be- 
tween two  cakes  M  M  of 
a  mixture  of  black  oxide 
of  manganese,  sulphur, 
and  carbon,  plunged  in  a 
solution  of  sal  ammoniac. 
The  oxide  of  manganese 
relieves  the  carbon  plate 
of  its  hydrogen.  The 
strength  of  the  solution 
is  maintained  by  spare 
crystals  of  sal  ammoniac 
lying  on  the  bottom  of 
the  cell,  which  is  closed 
to  prevent  evaporation, 
but  has  a  venthole  for 
the  escape  of  gas. 
The  Bichromate  of  Potash  cell  polarises  more 
than  the  Leclanche,  but  yields  a  more  powerful 
current  for  a  short  time.  It  consists,  as  shown 
in  figure  17,  of  a  zinc  plate  Z  between  two  carbon 
plates  C  C  immersed  in  a  solution  of  bichromate 
of  potash,  sulphuric  acid  (vitriol),  and  water.  The 
zinc  is  always  lifted  out  of  the  solution  when  the 
cell  is  not  in  use.  The  gas  which  collects  in  the 


FIG.  16.— The  Leclanche  Cell. 


THE  ELECTRICITY  OF  CHEMISTRY. 


35 


test- 
The 


carbons,  and  weakens  the  cell,  can  be  set  free  by 
raising  the  plates  out  of  the  liquid  when  the  cell 
is  not  wanted.  Stirring  the  solution  has  a  similar 
effect,  and  sometimes  the  constancy  of  the  cell  is 
maintained  by  a  circulation  of  the  liquid.  In 
Fuller's  bichromate  cell  the  zinc  is  amalgamated 
with  mercury,  which  is  kept  in  a  pool  beside  it 
by  means  of  a  porous  pot. 

De  la  Rue's  chloride  of  silver  cell  (fig.   18) 

is,     from     its 

constancy  and 

small  size,  well 

adapted       for 

medical     and 

ing  purposes. 

"plates  "are  a  little 

rod  or  pencil  of  zinc 

Z,  and  a  strip  or  wire 

of   silver  S,  coated 

with  chloride  of  sil- 
ver    and     sheathed 

in  parchment  paper. 

They    are    plunged 

in     a     solution     of 

ammonium  chloride 

A,  contained  in  a 
glass  phial  or  beaker,  which  is  closed  to  sup- 
press evaporation.  A  tray  form  of  the  cell  is 
also  made  by  laying  a  sheet  of  silver  foil  on 
the  bottom  of  the  shallow  jar,  and  strewing  it 
with  dry  chloride  of  silver,  on  which  is  laid 
a  jelly  to  support  the  zinc  plate.  The  jelly  is 
prepared  by  mixing  a  solution  of  chloride  of  am- 
monium with  "agar-agar,"  or  Ceylon  moss.  This 
type  permits  the  use  of  larger  plates,  and  adapts 
the  battery  for  lighting  small  electric  lamps. 


FIG.  17.— The 
Bichromate  Cell. 


FIG.  18. 

The  Chloride  of 

Silver  Cell. 


36  THE  STORY   OF   ELECTRICITY. 

Skrivanoff  has  modified  the  De  la  Rue  cell  by 
substituting  a  solution  of  caustic  potash  for  the 
ammonium  chloride,  and  his  battery  has  been 
used  for  "  star  "  lights,  that  is  to  say,  the  tiny 
electric  lamps  of  the  ballet.  The  Schanschieff 
battery,  consisting  of  zinc  and  carbon  plates  in 
a  solution  of  basic  sulphate  of  mercury,  is  suit- 
able for  reading,  mining,  and  other  portable 
lamps. 

The  Latimer  Clark  "  standard  "  cell  is  used  by 
electricians  in  testing,  as  a  constant  electromotive 
force.  It  consists  of  a  pure  zinc  plate  separated 
from  a  pool  of  mercury  by  a  paste  of  mercurous 
proto-sulphate  and  saturated  solution  of  sulphate 
of  zinc.  Platinum  wires  connect  with  the  zinc" 
and  mercury  and  form  the  poles  of  the  battery, 
and  the  mouth  of  the  glass  cell  is  plugged  with 
solid  paraffin.  As  it  is  apt  to  polarise,  the  cell 
must  not  be  employed  to  yield  a  current,  and 
otherwise  much  care  should  be  taken  of  it. 

Dry  cells  are  more  cleanly  and  portable  than 
wet,  they  require  little  or  no  attention,  and  are 
well  suited  for  household  or  medical  purposes. 
The  zinc  plate  forms  the  vessel  containing  the 
carbon  plate  and  chemical  reagents.  Figure  19 
represents  a  section  of  the  "  E.  C.  C."  variety, 
where  Z  is  the  zinc  standing  on  an  insulating 
sole  /,  and  fitted  with  a  connecting  wire  or 
terminal  T  (  — ),  which  is  the  negative  pole.  The 
carbon  C  is  embedded  in  black  paste  M,  chiefly 
composed  of  manganese  dioxide,  and  has  a  bind- 
ing screw  or  terminal  T  (+),  which  is  the  posi- 
tive pole.  The  black  paste  is  surrounded  by  a 
white  paste  Z,  consisting  mainly  of  lime  and  sal- 
ammoniac.  There  is  a  layer  of  silicate  cotton 
S  C  above  the  paste,  and  the  mouth  is  sealed  with 


THE   ELECTRICITY  OF   CHEMISTRY. 


37 


black  pitch  JP9  through  which  a  waste-tube  W  T 
allows  the  gas  to  escape. 

The  Hellesen  dry  cell  is  like  the  "  E.  C.  C.," 
but  contains  a 
hollow  carbon, 
and  is  packed 
sawdust 
millboard 


T(-H 


with 
in  a 

case.  The  Le- 
clanche-Barbier 
dry  cell  is  a 
modification  of 
the  Leclanche* 
wet  cell,  having 
a  paste  of  sal- 
ammoniac  in- 
stead of  a  so- 
lution. 

All  the  fore- 
going cells  are 
called  "  prima- 
ry/' because 
they  are  gener- 
ators of  electri- 
city. There  are,  however,  batteries  known  as  "  sec- 
ondary," which  store  the  current  as  the  Leyden 
jar  stores  up  the  discharge  from  an  electrical 
machine. 

In  the  action  of  a  primary  cell,  as  we  have 
seen,  water  is  split  into  its  constituent  gases, 
oxygen  and  hydrogen.  Moreover,  it  was  dis- 
covered by  Carlisle  and  Nicholson  in  the  year 
1800  that  the  current  of  a  battery  could  de- 
compose water  in  the  outer  part  of  the  circuit. 
Their  experiment  is  usually  performed  by  the 
apparatus  shown  in  figure  20,  which  is  termed  a 


i 


FIG.  19.— The  E.  C.  C.  Dry  Cell. 


38  THE  STORY  OF  ELECTRICITY. 

voltameter,  and  consists  of  a  glass  vessel  V,  con- 
taining water  acidulated  with  a  little  sulphuric 
acid  to  render  it  a  better  conductor,  and  two  glass 
test-tubes  OH  inverted  over  two  platinum  strips 
or  electrodes,  which  rise  up  from  the  bottom  of 
the  vessel  and  are  connected  underneath  it  to 
wires  from  the  positive  and  negative  poles  of  the 
battery  C  Z.  It  will  be  understood  that  the  cur- 


FIG.  20.— The  Voltameter. 

rent  enters  the  water  by  the  positive  electrode, 
and  leaves  it  by  the  negative  electrode. 

When  the  power  of  the  battery  is  sufficient  the 
water  in  the  vessel  is  decomposed,  and  oxygen 
being  the  negative  element, ^collects  at  the  posi- 
tive foil  or  electrode,  which  is  covered  by  the 
tube  O.  The  hydrogen,  on  the  other  hand,  being 
positive,  collects  at  the  negative  foil  under  the 
tube  H.  These  facts  can  be  proved  by  dipping 
a  red-hot  wick  or  taper  into  the  gas  of  the  tube 
O  and  seeing  it  blaze  in  presence  of  the  oxygen 
which  feeds  the  combustion,  then  dipping  the 


THE  ELECTRICITY  OF  CHEMISTRY.  39 

lighted  taper  into  the  gas  of  the  tube  H  and 
watching  it  burn  with  the  blue  flame  of  hydro- 
gen. The  volume  of  gas  at  the  cathode  or  nega- 
tive electrode  is  always  twice  that  at  the  anode  or 
positive  electrode,  as  it  should  be  according  to 
the  known  composition  of  water. 

Now,  if  we  disconnect  the  battery  and  join  the 
two  platinum  electrodes  of  the  voltameter  by  a 
wire,  we  shall  find  a  current  flowing  out  of  the 
voltameter  as  though  it  were  a  battery,  but  in 
the  reverse  direction  to  the  original  current  which 
decomposed  the  water.  This  "  secondary  "  or  re- 
acting current  is  evidently  due  to  the  polar- 
isation "  of  the  foils— that  is  to  say,  the  electro- 
positive and  electro-negative  gases  collected  on 
them. 

Professor  Groves  constructed  a  gas  battery 
on  this  principle,  the  plates  being  of  platinum 
and  the  two  gases  surrounding  them  oxygen  and 
hydrogen,  but  the  most  useful  development  of  it 
is  the  accumulator  or  storage  battery. 

The  first  practicable  secondary  battery  of 
Gaston  Plante  was  made  of  sheet  lead  plates 
or  electrodes,  kept  apart  by  linen  cloth  soaked 
in  dilute  sulphuric  acid,  after  the  manner  of 
Volta's  pile.  It  was  "  charged  "  by  connecting 
the  plates  to  a  primary  battery,  and  peroxide  of 
lead  (Pb  O2)  was  formed  on  one  plate  and  spongy 
lead  (Pb)  on  the  other.  When  the  charging  cur- 
rent was  cut  off  the  peroxide  plate  became  the 
positive  and  the  spongy  plate  the  negative  pole 
of  the  secondary  cell. 

Faure  improved  the  Plante*  cell  by  adding  a 
paste  of  red  lead  or  minium  (Pb2  O±)  and  dilute 
sulphuric  acid  (H2  SO^),  by  which  a  large  quan- 
tity of  peroxide  and  spongy  lead  could  be  formed 


40  THE   STORY  OF  ELECTRICITY. 

on  the  plates.  Sellon  and  Volckmar  increased 
its  efficiency  by  putting  the  paste  into  holes  cast 
in  the  lead.  The  "  E.  P.  S."  accumulator  of  the 
Electrical  Power  Storage  Company  is  illustrated 
in  figure  21,  and  consists  of  a  glass  or  teak  box 


FIG.  2i.— The  E.  P.  S.  Accumulator. 


containing  two  sets  of  leaden  grids  perforated 
with  holes,  which  are  primed  with  the  paste  and 
steeped  in  dilute  sulphuric  acid.  Alternate  grids 
are  joined  to  the  poles  of  a  charging  battery  or 
generator,  those  connected  to  the  positive  pole 
being  converted  into  peroxide  of  lead  and  the 
others  into  spongy  lead.  The  terminal  of  the 
peroxide  plates,  being  the  positive  pole  of  the 
accumulator,  is  painted  red,  and  that  of  the 
spongy  plates  or  negative  pole  black.  Accumu- 
lators of  this  kind  are  highly  useful  as  reservoirs 
of  electricity  for  maintaining  the  electric  light,  or 
working  electric  motors  in  tramcars,  boats,  and 
other  carriages. 


THE   ELECTRICITY  OF   HEAT.  41 

CHAPTER   III. 

THE    ELECTRICITY    OF    HEAT. 

IN  the  year  1821  Professor  Seebeck,  of  Ber- 
lin, discovered  a  third  source  of  electricity.  Volta 
had  found  that  two  dissimilar  metals  in  contact 
will  produce  a  current  by  chemical  action,  and 
Seebeck  showed  that  heat  might  take  the  place 
of  chemical  action.  Thus,  if  a  bar  of  antimony 
A  (fig.  22)  and  a  bar  of  bismuth  B  are  in  contact 
at  one  end,  and  the  junc- 
tion is  heated  by  a  spirit 
lamp  to  a  higher  tempera- 
ture than  the  rest  of  the 
bars,  a  difference  in  their 
electric  state  or  potential 
will  be  set  up,  and  if  the 
other  ends  are  joined  by  a 
wire  W,  a  current  will  flow  FlG  22 

through  the  wire.  The  di-  A  Thermo-electric  Couple. 
rection  of  the  current,  in- 
dicated by  the  arrow,  is  from  the  bismuth  to  the 
antimony  across  the  joint,  and  from  the  antimony 
to  the  bismuth  through  the  external  wire.  This 
combination,  which  is  called  a  "  thermo-electric 
couple,"  is  clearly  analogous  to  the  voltaic  couple, 
with  heat  in  place  of  chemical  affinity.  The  direc- 
tion of  the  current  within  and  without  the  couple 
shows  that  the  bismuth  is  positive  to  the  antimony. 
This  property  of  generating  a  current  of  elec- 
tricity by  contact  under  the  influence  of  heat  is 
not  confined  to  bismuth  and  antimony,  or  even 
to  the  metals,  but  is  common  to  all  dissimilar 
substances  in  their  degree.  In  the  following  list 
of  bodies  each  is  positive  to  those  beneath  it, 


42  THE  STORY  OF  ELECTRICITY. 

negative  to  those  above  it,  and  the  further  apart 
any  two  are  in  the  scale  the  greater  the  effect. 
Thus  bismuth  and  antimony  give  a  much  stronger 
current  with  the  same  heating  than  copper  and 
iron.  Bismuth  and  selenium  produce  the  best 
result,  but  selenium  is  expensive  and  not  easy  to 
manipulate.  Copper  and  German  silver  will  make 
a  cheap  experimental  couple : — 
POSITIVE. 

Bismuth. 

Cobalt. 

Potassium. 

Nickel. 

Sodium. 

Lead. 

Tin. 

Copper. 

Platinum. 

Silver, 

Zinc. 

Cadmium. 

Arsenic. 

Iron. 

Red  phosphorus. 

Antimony. 

Tellurium. 

Selenium. 
NEGATIVE. 

Other  things  being  equal,  the  hotter  the  joint 
in  comparison  with  the  free  ends  of  the  bars  the 
stronger  the  current  of  electricity.  Within  cer- 
tain limits  the  current  is,  in  fact,  proportional  to 
this  difference  of  temperature.  It  always  flows 
in  the  same  direction  if  the  joint  is  not  over- 
heated, or,  in  other  words,  raised  above  a  certain 
temperature. 


THE   ELECTRICITY  OF   HEAT.  43 

The  electromotive  force  and-  current  of  a 
thermo-electric  couple  is  very  much  smaller  than 
that  given  by  an  ordinary  voltaic  cell.  We  can, 
however,  multiply  the  effect  by  connecting  a 
number  of  pairs  together,  and  so  forming  a  pile 
or  battery.  Thus  figure  23  shows  three  couples 
joined  "in  series,"  the  positive  pole  of  one  being 
connected  to  the  negative  pole  of  the  next.  Now, 
if  all  the  junctions  on  the  left  are  hot  and  those 
on  the  right  are  cool,  we  will  get  the  united  effect 
of  the  whole,  and  the  total 
current  will  flow  through 
the  wire  W,  joining  the  ex- 
treme  bars  or  positive  and 
negative  poles  of  the  bat- 
tery. It  must  be  borne  in 
mind  that  although  the  bis- 
muth and  antimony  of  this 
thermo-electric  battery,  like 
the  zinc  and  copper  of  FlG.  23_™ermo_electric 
the  voltaic  or  chemiCO-  Couples  in  Series. 

electric  battery,  are  re- 
spectively positive  and  negative  to  each  other, 
the  poles  or  wires  attached  to  these  metals  are, 
on  the  contrary,  negative  and  positive.  This 
peculiarity  arises  from  the  current  starting  be- 
tween the  bismuth  and  antimony  at  the  heated 
junction. 

The  internal  resistance  of  a  "  thermo-electric 
pile  "  is,  of  course,  very  slight,  the  metals  being 
good  conductors,  and  this  fact  gives  it  a  certain 
advantage  over  the  voltaic  battery.  Moreover, 
it  is  cleaner  and  less  troublesome  than  the  chemi- 
cal battery,  for  it  is  only  necessary  to  keep  up 
the  required  difference  of  temperature  between 
the  hot  and  cold  junctions  in  order  to  get  a 


44 


THE   STORY  OF  ELECTRICITY. 


steady  current.-  No  solutions  or  salts  are  re- 
quired, and  there  appears  to  be  little  or  no  waste 
of  the  metals.  It  is  important,  however,  to  avoid 
sudden  heating  and  cooling  of  the  joints,  as  this 
tends  to  destroy  them. 

Clammond,  Glilcher,  and  others  have  con- 
structed useful  thermo-piles  for  practical  pur- 
poses. Figure  24  illus- 
trates a  Clammond  ther- 
mo-pile  of  75  couples  or 
elements.  The  metals 
forming  these  pairs  are 
an  alloy  of  bismuth  and 
antimony  for  one  and 
iron  for  the  other. 
Prisms  of  the  alloy  are 
cast  on  strips  of  iron 
to  form  the  junctions. 
They  are  bent  in  rings,- 
the  junctions  in  a  series 
making  a  zig-zag  round 
the  circle.  \  The  rings 
are  built  one  over  the  other  in  a  cylinder  of 
couples,  and  the  inner  junctions  are  heated  by 
a  Bunsen  gas-burner  in  the  hollow  core  of  the 
battery.  A  gas-pipe  seen  in  front  leads  to  the 
burner,  and  the  wires  WW  connected  to  the  ex- 
treme bars  or  poles  are  the  electrodes  of  the  pile. 
Thermo-piles  are  interesting  from  a  scientific 
point  of  view  as  a  direct  means  of  transforming 
heat  into  electricity.  A  sensitive  pile  is  also  a 
delicate  detector  of  heat  by  virtue  of  the  current 
set  up,  which  can  be  measured  with  a  galvan- 
ometer or  current  meter.  Piles  of  antimony  and 
bismuth  are  made  which  can  indicate  the  heat 
of  a  lighted  match  at  a  distance  of  several 


FIG.  24. 
A  Thermo-electric  Pile. 


THE   ELECTRICITY  OF   HEAT.  45 

yards,  and  even  the  radiation  from  certain  of  the 
stars. 

Thermo-batteries  have  been  used  in  France 
for  working  telegraphs,  and  they  are  capable  of 
supplying  small  installations  of  the  electric  light 
or  electric  motors  for  domestic  purposes. 

The  action  of  the  thermo-pile,  like  that  of  a 
voltaic  cell,  can  be  reversed.  By  sending  a  cur- 
rent through  the  couple  from  the  antimony  to  the 
bismuth  we  shall  find  the  junction  cooled.  This 
"JWtier^effgjfcfc^'  as  it  is  termed,  after  its  dis- 
coverer, has  been  known  to  freeze  water,  but  no 
practical  application  has  been  made  of  it. 

A  very  feeble  thermo-electric  effect  can  be 
produced  by  heating  the  junction  of  two  different 
pieces  of  the  same  substance,  or  even  by  making 
one  part  of  the  same  conductor  hotter  than 
another.  Thus  a  sensitive  galvanometer  will 
show  a  weak  current  if  a  copper  wire  connected 
in  circuit  with  it  be  warmed  at  one  point.  More- 
over, it  has  been  found  by  Lord  Kelvin  that  if  an 
iron  wire  is  heated  at  any  point,  and  an  electric 
current  be  passed  through  it,  the  hot  point  will 
shift  along  the  wire  in  a  direction  contrary  to 
that  of  the  current. 


CHAPTER   IV. 

THE    ELECTRICITY    OF    MAGNETISM. 

WE  have  already  seen  how  electricity  was  first 
produced  by  the  simple  method  of  rubbing  one 
body  on  another,  then  by  the  less  obvious  means 
of  chemical  union,  and  next  by  the  finer  agency 


46  THE  STORY  OF  ELECTRICITY. 

of  heat.  In  all  these,  it  will  be  observed,  a  sub- 
stantial contact  is  necessary.  We  have  now  to 
consider  a  still  more  subtle  process  of  generation, 
not  requiring  actual  contact,  which,  as  might  be 
expected,  was  discovered  later,  that,  mainly 
through  the  medium  of  magnetism. 

The  curious  mineral  which  has  the  property 
of  attracting  iron  was  known  to  the  Chinese 
several  thousand  years  ago,  and  certainty  to  the 
Greeks  in  the  times  of  Thales,  who,  as  in  the 
case  of  the  rubbed  amber,  ascribed  the  property 
to  its  possession  of  a  soul. 

Lodestone,  a  magnetic  oxide  of  iron  (Fe$  6>4), 
is  found  in  various  parts  of  China,  especially  at 
T'szchou  in  Southern  Chihli,  which  was  formerly 
known  as  the  "  City  of  the  Magnet."  It  was 
called  by  the  Chinese  the  love-stone  or  thsu-chy, 
and  the  stone  that  snatches  iron  or  ny-thy-chy, 
and  perchance  its  property  of  pointing  out  the 
north  and  south  direction  was  discovered  by  drop- 
ping a  light  piece  of  the  stone,  if  not  a  sewing 
needle  made  of  it,  on  the  surface  of  still  water. 
At  all  events,  we  read  in  Pere  Du  Halde's  Descrip- 
tion de  la  Chine,  that  sometime  in  or  about  the  year 
2635  B.  c.  the  great  Emperor  Hoang-ti,  having  lost 
his  way  in  a  fog  whilst  pursuing  the  rebellious 
Prince  Tchiyeou  on  the  plains  of  Tchou-lou,  con- 
structed a  chariot  which  showed  the  cardinal 
points,  thus  enabling  him  to  overtake  and  put  the 
prince  to  death. 

A  magnetic  car  preceded  the  Emperors  of 
China  in  ceremonies  of  state  during  the  fourth 
century  of  our  era.  It  contained  a  genius  in  a 
feather  dress  who  pointed  to  the  south,  and  was 
doubtless  moved  by  a  magnet  floating  in  water 
or  turning  on  a  pivot.  This  rude  appliance  was 


THE   ELECTRICITY  OF   MAGNETISM.  47 

afterwards  refined  into  the  needle  compass  for 
guiding  mariners  on  the  sea,  and  assisting  the 
professors  of  feng-shui  or  geomancy  in  their 
magic  rites. 

Magnetite  was  also  found  at  Heraclea  in 
Lydia,  and  at  Magnesium  on  the  Meander  or 
Magnesium  at  Sipylos,  all  in  Asia  Minor.  It  was 
called  the  "  Heraclean  Stone  "  by  the  people,  but 
came  at  length  to  bear  the  name  of  "  Magnet " 
after  the  city  of  Magnesia  or  the  mythical  shep- 
herd Magnes,  who  was  said  to  have  discovered  it 
by  the  attraction  of  his  iron  crook. 

The  ancients  knew  that  it  had  the  power  of 
communicating  its  attractive  property  to  iron,  for 
we  read  in  Plato's  "  Ion  "  that  a  number  of  iron 
rings  can  be  supported  in  a  chain  by  the  Hera- 
clean  Stone.  Lucretius  also  describes  an  experi- 
ment in  which  iron  filings  are  made  to  rise  up 
and  "  rave  "  in  a  brass  basin  by  a  magnet  held 
underneath.  We  are  told  by  other  writers  that 
images  of  the  gods  and  goddesses  were  suspended 
in  the  air  by  lodestone  in  the  ceilings  of  the 
temples  of  Diana  of  Ephesus,  of  Serapis  at  Alex- 
andria, and  others.  It  is  surprising,  however, 
that  neither  the  Greeks  nor  Romans,  with  all 
their  philosophy,  would  seem  to  have  discovered 
its  directive  property. 

During  the  dark  ages  pieces  of  lodestone 
mounted  as  magnets  were  employed  in  the  "black 
arts."  A  small  natural  magnet  of  this  kind  is 
shown  in  figure  25,  where  L  is  the  stone  shod 
with  two  iron  "  pole-pieces,"  which  are  joined  by 
a  "  keeper  "  A  or  separable  bridge  of  iron  carry- 
ing a  hook  for  supporting  weights. 

Apparently  it  was  not  until  the  twelfth  cen- 
tury that  the  compass  found  its  way  into  Europe 


48 


THE  STORY  OF   ELECTRICITY. 


from  the  East.  In  the  Landnammabok  of  Ari 
Frode,  the  Norse  historian,  we  read  that  Flocke 
Vildergersen,  a  renowned  viking,  sailed  from 
Norway  to  discover  Iceland  in  the  year  868,  and 
took  with  him  two  ravens  as  guides,  for  in  those 
days  the  "  seamen  had  no  lodestone  (that  is,  no 
lidar  stein,  or  leading  stone)  in  the  northern 
countries."  The  Bible,  a  poem  of  Guiot  de  Pro- 
vins,  minstrel  at  the  court  of  Barbarossa,  which 
was  written  in  or  about  the  year  1190,  contains 
the  first  mention  of  the  magnet  in  the  West. 
Guiot  relates  how  mariners  have  an  "  art  which 
cannot  deceive "  of  finding  the  position  of  the 
polestar,  that  does  not  move. 
After  touching  a  needle  with 
the  magnet,  "  an  ugly  brown 
stone  which  draws  iron  to 
itself,"  he  says  they  put  the 
needle  on  a  straw  and  float  it 
on  water  so  that  its  point 
turns  to  the  hidden  star,  and 
enables  them  to  keep  their 
course.  Arab  traders  had 
probably  borrowed  the  float- 
ing needle  from  the  Chinese, 
for  Bailak  Kibdjaki,  author 
of  the  Merchant's  Treasure, 
written  in  the  thirteenth  cen- 
tury, speaks  of  its  use  in  the 
Syrian  sea.  The  first  Cru- 
saders were  probably  instru- 
mental in  bringing  it  to  France,  at  all  events 
Jacobus  de  Vitry  (1204-15)  and  Vincent  de  Beau- 
vais  (1250)  mention  its  use,  De  Beauvais  calling 
the  poles  of  the  needle  by  the  Arab  words  aphron 
and  zohron. 


FIG.  25. 
A  Natural  Magnet. 


THE   ELECTRICITY   OF   MAGNETISM.  49 

Ere  long  the  needle  was  mounted  on  a  pivot 
and  provided  with  a  moving  card  showing  the 
principal  directions.  The  variation  of  the  needle 
from  the  true  north  and  south  was  certainly 
known  in  China  during  the  twelfth,  and  in  Europe 
during  the  thirteenth  century.  Columbus  also 
found  that  the  variation  changed  its  value  as  he 
sailed  towards  America  on  his  memorable  voyage 
of  1492.  Moreover,  in  1576,  Norman,  a  compass 
maker  in  London,  showed  that  the  north-seeking 
end  of  the  needle  dipped  below  the  horizontal. 

In  these  early  days  it  was  supposed  that  lode- 
stone  in  the  pole-star,  that  is  to  say,  the  "  lode- 
star "  of  the  poets  or  in  mountains  of  the  far 
north,  attracted  the  trembling  needle  ;  but  in  the 
year  1600,  Dr.  Gilbert,  the  founder  of  electric 
science,  demonstrated  beyond  a  doubt  that  the 
whole  earth  was  a  great  magnet.  A  magnet,  as  is 
well  known,  has,  like  an  electric  battery,  always 
two  poles  or  centres  of  attraction,  which  are  situ- 
ated near  its  extremities.  Sometimes,  indeed, 
when  the  magnet  is  imperfect,  there  are  "  conse- 
quent poles "  of  weaker  force  between  them. 
One  of  the  poles  is  called  the  "  north,"  and  the 
other  the  "  south,"  because  if  the  magnet  were 
freely  pivotted  like  a  compass  needle,  the  former 
would  turn  to  the  north  and  the  latter  to  the 
south. 

Either  pole  will  attract  iron,  but  soft  or  an- 
nealed iron  does  not  retain  the  magnetism  nearly 
so  well  as  steel.  Hence  a  boy's  test  for  the  steel 
of  his  knife  is  only  efficacious  when  the  blade 
itself  becomes  magnetic  after  being  touched  with 
the  magnet.  A  piece  of  steel  is  readily  magnet- 
ised by  stroking  it  from  end  to  end  in  one  direc- 
tion with  the  pole  of  a  magnet,  and  in  this  way 
4 


THE   STORY  OF   ELECTRICITY. 


r\ 


compass  needles  and  powerful  bar  magnets  can 
be  made. 

The  poles  attract  iron  at  a  distance  by  "  in- 
duction," just  as  a  charge  of  electricity,  be  it 
positive  or  negative,  will  attract 
a  neutral  pith  ball ;  and  Dr.  Gil- 
bert showed  that  a  north  pole 
always  repels  another  north  pole 
and  attracts  a  south  pole,  while, 
on  the  other  hand, 
a  south  pole  always 
repels  a  south  pole 
and  attracts  a  north 
pole.  This  can  be 
proved  by  suspend- 
ing a  magnetic  nee- 
dle like  a  pithball, 
and  approaching  an- 
other towards  it,  as 
illustrated  in  figure 
26,  where  the  north 
pole  N  attracts  the  south  S.  Obviously  there 
are  two  opposite  kinds  of  magnetic  poles,  as 
of  electricity,  which  always  appear  together,  and 
like  magnetic  poles  repel,  unlike  magnetic  poles  at- 
tract each  other. 

It  follows  that  the  magnetic  pole  of  the 
compass  needle  which  turns  to  the  north  must 
be  unlike  the  north  and  like  the  south  magnetic 
pole  of  the  earth.  Instead  of  calling  it  the 
"  north,"  it  would  be  less  confusing  to  call  it 
the  "north-seeking"  pole  of  the  needle. 

Gilbert  made  a  "terella,"  or  miniature  of  the 
earth,  as  a  magnet,  and  not  only  demonstrated 
how  the  compass  needle  sets  along  the  lines 
joining  the  north  and  south  magnetic  poles,  but 


FIG.  26. 


THE  ELECTRICITY  OF  MAGNETISM.  51 

explained  the  variation  and  the  dip.  He  im- 
agined that  the  magnetic  poles  coincided  with 
the  geographical  poles,  but,  as  a  matter  of  fact, 
they  do  not,  and,  moreover,  they  are  slowly 
moving  round  the  geographical  poles,  hence  the 
declination  of  the  needle,  that  is  to  say  its  angle 
of  divergence  from  the  true  meridian  or  north 
and  south  line,  is  gradually  changing.  The 
north  magnetic  pole  of  the  earth  was  actually 
discovered  by  Sir  John  Ross  north  of  British 
America,  on  the  coast  of  Boothia  (latitude  70°  5' 
N.,  longitude  96°  46'  W.),  where,  as  foreseen,  the 
needle  entirely  lost  its  directive  property  and 
stood  upright,  or,  so  to  speak,  on  its  head.  The 
south  magnetic  pole  lies  in  the  Prince  Albert 
range  of  Victoria  Land,  and  was  almost  reached 
by  Sir  James  Clark  Ross. 

The  magnetism  of  the  earth  is  such  as  might 
be  produced  by  a  powerful  magnet  inside,  but  its 
origin  is  unknown,  although  there  is  reason  to 
believe  that  masses  of  lodestone  or  magnetic  iron 
exist  in  the  crust.  Coulomb  found  that  not  only 
iron,  but  all  substances  are  more  or  less  magnetic, 
and  Faraday  showed  in  18^5  that  while  some  are 
attracted  by  a  magnet  others  are  repelled.  The 
former  he  called  paramagnetic  and  the  latter  dia- 
magnetic  bodies. 

The  following  is  a  list  of  these  : — 

Paramagnetic.  Diamagnetic. 

Iron.  Bismuth. 

M.  ,    ,  Phosphorus. 

jNlckel-  Antimony. 

Cobalt.  Zinc- 

Mercury. 

Aluminium.  Lead. 


£2  THE   STORY   OF   ELECTRICITY, 

Manganese.  Silver. 

Chromium,  n  v? 

Gold. 

Cerium.  Water. 

Titanium.  Alcohol. 

Platinum.  Tellurium. 

Many    ores  and                          Selenium. 

r  ,                             Sulphur. 

salts      of  the                         Thallium. 

above  metals.  Hydrogen. 

Oxygen.  Air. 

We  have  theories  of  magnetism  that  reduce 
it  to  a  phenomenon  of  electricity,  though  we  are 
ignorant  of  the  real  nature  of  both.  If  we  take 
a  thin  bar  magnet  and  break  it  in  two,  we  find 
that  we  have  now  two  shorter  magnets,  each  with 
its  "  north  "  and  "  south  "  poles,  that  is  to  say, 
poles  of  the  same  kind  as  the  south  and  north 
magnetic  poles  of  the  earth.  If  we  break  each  of 
these  again,  we  get  four  smaller  magnets,  and  we 
can  repeat  the  process  as  often  as  we  like.  It  is 
supposed,  therefore,  that  every  atom  of  the  bar  is 
a  little  magnet  in  itself  having  its  two  opposite 
poles,  and  that  in  magnetising  the  bar  we  have 
merely  partially  turned  all  these  atoms  in  one 
direction,  that  is  to  say,  with  their  north  poles 
pointing  one  way  and  their  south  poles  the  other 
way,  as  shown  in  figure  27.  The  polarity  of  the 
bar  only  shows  itself  at  the  ends,  where  the  molec- 
ular poles  are,  so  to  speak,  free. 

There  are  many  experiments  which  support 
this  view.  For  example,  if  we  heat  a  magnet 
red  hot  it  loses  its  magnetism,  perhaps  because 
the  heat  has  disarranged  the  particles  and  set 
the  molecular  poles  in  all  directions.  Again,  if 


THE   ELECTRICITY  OF  MAGNETISM.  53 

we  magnetise  a  piece  of  soft  iron  we  can  destroy 
its  magnetism  by  striking  it  so  as  to  agitate  its 
atoms  and  throw  them  out  of  line.  In  steel, 
which  is  iron  with  a  small  admixture  of  carbon, 
the  atoms  are  not  so  free  as  in  soft  iron,  and 
hence,  while  iron  easily  loses  its  magnetism,  steel 


mm i  linn i  HUD i   muni  unin  niroi  nniii 
""Ml  mm  i    mm  PTflin  f   mm  i    uumi   iinjif 

imiif  mill  i  limit  iiiiiinrnnf  immmrnif 


S     N  F.0.27. 

retains  it,  even  under  a  shock,  but  not  under  a 
cherry  red-heat.  Nevertheless,  if  we  put  the 
atoms  of  soft  iron  under  a  strain  by  bending  it, 
we  shall  find  it  retain  its  magnetism  more  like  a 
bit  of  steel. 

It  has  been  found,  too,  that  the  atoms  show 
an  indisposition  to  be  moved  by  the  magnetising 
force  which  is  known  as  hysteresis.  They  have  a 
certain  inertia,  which  can  be  overcome  by  a  slight 
shock,  as  though  they  had  a  difficulty  of  turning 
in  the  ranks  to  take  up  their  new  positions. 
Even  if  this  molecular  theory  is  true,  however, 
it  does  not  help  us  to  explain  why  a  molecule  of 
matter  is  a  tiny  magnet.  We  have  only  pushed 
the  mystery  back  to  the  atom.  Something  more 
is  wanted,  and  electricians  look  for  it  in  the  con- 
stitution of  the  atom,  and  in  the  luminiferous 
ether  which  is  believed  to  surround  the  atoms  of 
matter,  and  to  propagate  not  merely  the  waves 
of  light,  but  induction  from  one  electrified  body 
to  another. 

We  know  in  proof  of  this  ethereal  action  that 
the  space  around  a  magnet  is  magnetic.  Thus, 
if  we  lay  a  horse-shoe  magnet  on  a  table  and 


54 


THE   STORY   OF   ELECTRICITY. 


sprinkle  iron  filings  round  it,  they  will  arrange 
themselves  in  curving  lines  between  the  poles  as 
shown  in  figure  28.  Each  filing  has  become  a 
little  magnet,  and  these 
set  themselves  end  to 
end  as  the  molecules  in 
the  metal  are  supposed 
to  do.  The  "field" 
about  the  magnet  is  re- 
plete with  these  lines, 
which  follow  certain 
curves  depending  on  the 
arrangement  of  the  poles. 
In  the  horse-shoe  magnet, 
as  seen,  they  chiefly  issue 
from  one  pole  and  sweep 
round  to  the  other. 
They  are  never  broken, 
and  apparently  they  are 
lines  of  stress  in  the 
circumambient  ether.  A 
pivoted  magnet  tends  to 
range  itself  along  these 
FIG.  28.  lines,  and  thus  the  com- 

pass guides  the  sailor  on 

the  ocean  by  keeping  itself  in  the  line  between 
the  north  and  south  magnetic  poles  of  the  earth. 
Faraday  called  them  lines  of  magnetic  force ',  and 
said  that  £he  stronger  the  magnet  the  more  of 
these  li^es  pass  through  a  given  space.  Along 
them  "  magnetic  induction  "  is  supposed  to  be 
propagated,  and  a  magnet  is  thus  enabled  to  attract 
Von  or  any  other  magnetic  substance.  The  pole 
induces  an  opposite  pole  to  itself  in  the  nearest 
part  of  the  induced  body  and  a  like  pole  in  the 
remote  part.  Consequently,  as  unlike  poles  at- 


THE   ELECTRICITY   OF   MAGNETISM.  55 

tract  and  like  repel,  the  soft  iron  is  attracted  by 
the  inducing  pole  much  as  a  pithball  is  attracted 
by  an  electric  charge. 

The  resemblances  of  electricity  and  magnet- 
ism did  not  escape  attention,  and  the  derangement 
of  the  compass  needle  by  the  lightning  flash,  for- 
merly so  disastrous  at  sea,  pointed  to  an  intimate 
connection  between  them,  which  was  ultimately 
disclosed  by  Professor  Oersted,  of  Copenhagen, 
in  the  year  1820.  Oersted  was  on  the  outlook 
for  the  required  clue,  and  a  happy  chance  is  said 
to  have  rewarded  him.  His  experiment  is  shown 
in  figure  29,  where  a  wire  conveying  a  current  of 


FIG.  29. 

electricity  flowing  in  the  direction  of  the  arrow 
is  held  over  a  pivoted  magnetic  needle  so  that 
the  current  flows  from  south  to  north.  The 
needle  will  tend  to  set  itself  at  right  angles  to 
the  wire,  its  north  or  north-seeking  pole  moving 
towards  the  west.  If  the  direction  of  the  current 
is  reversed,  the  needle  is  deflected  in  the  opposite 


56  THE   STORY  OF   ELECTRICITY. 

direction,  its  north  pole  moving  towards  the  east. 
Further,  if  the  wire  is  held  below  the  needle,  in 
the  first  place,  the  north  pole  will  turn  towards 
the  east,  and  if  the  current  be  reversed  it  will 
move  towards  the  west. 

The  direction  of  a  current  can  thus  be  told 
with  the  aid  of  a  compass  needle.  When  the  wire 
is  wound  many  times  round  the  needle  on  a  bob- 
bin, the  whole  forms  what  is  called  a  galvano- 
scope,  as  shown  in  figure  30,  where  N  is  the 


FIG.  30.— The  Galvanoscope. 

needle  and  B  the  bobbin.  When  a  proper  scale 
is  added  to  the  needle  by  which  its  deflections 
can  be  accurately  read,  the  instrument  becomes  a 
current  measurer  or  galvanometer,  for  within  cer- 
tain limits  the  deflection  of  the  needle  is  propor- 
tional to  the  strength  of  the  current  in  the  wire. 

A  rule  commonly  given  for  remembering  the 
movement  of  the  needle  is  as  follows  : — Imagine 
yourself  laid  along  the  wire  so  that  the  current 
flows  from  your  feet  to  your  head ;  then  if  you 
face  the  needle  you  will  see  its  north  pole  go  to 
the  left  and  its  south  pole  to  the  right.  I  find  it 
simpler  to  recollect  that  if  the  current  flows  from 
your  head  to  your  feet  a  north  pole  will  move 
round  you  from  left  to  right  in  front.  Or,  again, 
if  a  current  flows  from  north  to  south,  a  north 


THE   ELECTRICITY  OF   MAGNETISM.  57 

pole  will  move  round  it  like  the  sun  round  the 
earth. 

The  influence  of  the  current  on  the  needle 
implies  a  magnetic  action,  and  if  we  dust  iron 
filings  around  the  wire  we  shall  find  they  cling  to 
it  in  concentric  layers,  showing  that  circular  lines 
of  magnetic  force  enclose  it  like  the  water  waves 
caused  by  a  stone  dropped  into  a  pond.  Figure 
31  represents  the  section  of  a  wire  carrying  a 
current,  with  the  iron  filings 
arranged  in  circles  round  it. 
Since  a  magnetic  pole  tends  to 
move  in  the  direction  of  the 
lines  of  force,  we  now  see  why 

a  north  or  south  pole  tends  to   

move  round  a  current,  and  why  FIG.  31. 

a  compass  needle  tries  to  set 
itself  at  right  angles  to  a  current,  as  in  the  original 
experiment  of  Oersted.  The  needle,  having  two 
opposite  poles,  is  pulled  in  opposite  directions  by 
the  lines,  and  being  pivoted,  sets  itself  tangenti- 
cally  to  them.  Were  it  free  and  flexible,  it  would 
curve  itself  along  one  of  the  lines.  Did  it  consist 
of  a  single  pole,  it  would  revolve  round  the  wire. 

Action  and  re-action  are  equal  and  opposite, 
hence  if  the  needle  is  fixed  and  the  wire  free  the 
current  will  move  round  the  magnet ;  and  if 
both  are  free  they  will  circle  round  each  other. 
Applying  the  above  rule  we  shall  find  that  when 
the  north  pole  moves  from  left  to  right  the  cur- 
rent moves  from  right  to  left.  Ampere  of  Paris, 
following  Oersted,  promptly  showed  that  two 
parallel  wires  carrying  currents  attracted  each 
other  when  the  currents  flowed  in  the  same  direc- 
tion, and  repelled  each  other  when  they  flowed  in 
opposite  directions.  Thus,  in  figure  32,  if  A  and 


THE   STORY   OF   ELECTRICITY. 


B  are  the  two  parallel  wires,  and  A  is  mounted 
on  pivots  and  free  to  move  in  liquid  "  contacts  " 
of  mercury,  it  will  be  attracted  or  repelled  by  B 
according  as  the  two  currents  flow  in  the  same  or 
in  opposite  directions.  If  the  wires  cross  each 
other  at  right  angles  there  is  no  attraction  or  re- 
pulsion. If  they  cross  at  an  acute  angle,  they 
will  tend  to  become  parallel  like  two  compass 


B 


FIG.  32. 

needles,  when  the  currents  are  in  one  direction, 
and  to  open  to  a  right  angle  and  close  up  the 
other  way  when  the  currents  are  in  opposite 
directions,  always  tending  to  arrange  themselves 
parallel  and  flowing  in  the  same  direction.  These 


THE   ELECTRICITY   OF   MAGNETISM. 


59 


effects  arise  from  the  circular  lines  of  force 
around  the  wire.  When  the  currents  are  similar 
the  lines  act  as  unlike  magnetic  poles  and  attract, 
but  when  the  currents  are  dissimilar  the  lines  act 
as  like  magnetic  poles  and  repel  each  other. 

Another  important  discovery  of  Ampere  is 
that  a  circular  current  behaves  like  a  magnet ; 
and  it  has  been  suggested  by  him  that  the  atoms 
are  magnets  because  each  has  a  circular  current 
flowing  round  it.  A  series  of  circular  currents, 
such  as  the  spiral  S  in  figure  33  gives,  when  con- 
nected to  a  battery  C  Z,  is  in  fact  a  skeleton 


FIG.  33. 

electro-magnet  having  its  north  and  south  poles  at 
the  extremities.  If  a  rod  or  core  of  soft  iron  / 
be  suspended  by  fibres  from  a  support,  it  will  be 
sucked  towards  the  middle  of  the  coil  as  into  a 
vortex,  by  the  circular  magnetic  lines  of  every 
spire  or  turn  of  the  coil.  Such  a  combination  is 
sometimes  called  a  solenoid,  and  is  useful  in 
practice. 


6o 


THE  STORY  OF   ELECTRICITY. 


When  the  core  gains  the  interior  of  the  coil  it 
becomes  a  veritable  electromagnet,  as  found  by 
Arago,  having  a  north  pole  at  one  end  and  a 
south  pole  at  the  other.  Figure  34  illustrates  a 
common  poker  magnetised  in  the  same  way,  and 
supporting  nails  at  both  ends.  The  poker  has 


FIG.  34. 

become  the  core  of  the  electromagnet.  On  re- 
versing the  direction  of  the  current  through  the 
spiral  we  reverse  the  poles  of  the  core,  for  the 
poker  being  of  soft  or  wrought  iron,  does  not 
retain  its  magnetism  like  steel.  If  we  stop  the 
current  altogether  it  ceases  to  be  a  magnet,  and 
the  nails  will  drop  away  from  it. 

Ampere's  experiment  in  figure  32  has  shown  us 
that  two  currents,  more  or  less  parallel,  influence 
each  other;  but  in  1831  Professor  Faraday  of  the 
Royal  Institution,  London,  also  found  that  when 
a  current  is  started  and  stopped  in  a  wire,  it  in- 
duces a  momentary  and  opposite  current  in  a 
parallel  wire.  Thus,  if  a  current  is  started  in  the 
wire  B  (fig.  32)  in  direction  of  the  arrow,  it  will 
induce  or  give  rise  to  a  momentary  current  in 
the  wire  A,  flowing  in  a  contrary  direction  to 
itself.  Again,  if  the  current  in  B  be  stopped,  a 
momentary  current  is  set  up  in  the  wire  A  in  a 
direction  the  same  as  that  of  the  exciting  current 


THE   ELECTRICITY  OF   MAGNETISM. 


6l 


in  B.  While  the  current  in  B  is  quietly  flowing 
there  is  no  induced  current  in  A  ;  and  it  is  only 
at  the  start  or  the  stoppage  of  the  inducing  or 
primary  current  that  the  induced  or  secondary  cur- 
rent is  set  up.  Here  again  we  have  the  influence 
of  the  magnetic  field  around  the  wire  conveying 
a  current. 

This  is  the  principle  of  the  "  induction  coil  " 
so  much  employed  in  medical  electricity,  and  of 
the  "  transformer  "  or  "  converter  "  used  in  electric 
illumination.  It  consists  essentially,  as  shown  in 
figure  35,  of  two  coils  of  wire,  one  enclosing  the 
other,  and  both:  parallel  or  concentric.  The  inner 


FIG.  35. 


or  primary  coil  P  C  is  of  short  thick  wire  of  low 
resistance,  and  is  traversed  by  the  inducing  cur- 
rent of  a  battery  B.  To  increase  its  inductive 
effect  a  core  of  soft  iron  /  C  occupies  its  middle. 
The  outer  or  secondary  coil  S  C  is  of  long  thin 
wire  terminating  in  two  discharging  points  Z)1D2. 
An  interrupter  or  hammer  "key"  interrupts  or 
"  makes  and  breaks  "  the  circuit  of  the  primary 


62  THE   STORY   OF   ELECTRICITY. 

coil  very  rapidly,  so  as  to  excite  a  great  many 
induced  currents  in  the  secondary  coil  per  second, 
and  produce  energetic  sparks  between  the  ter- 
minals Dl  Dz.  The  interrupter  is  actuated  auto- 
matically by  the  magnetism  of  the  iron  core  /  C, 
for  the  hammer  H  has  a  soft  iron  head  which  is 
attracted  by  the  core  when  the  latter  is  magnet- 
ised, and  being  thus  drawn  away  from  the  con- 
tact screw  C  S  the  circuit  of  the  primary  is 
broken,  and  the  current  is  stopped.  The  iron 
core  then  ceases  to  be  a  magnet,  the  hammer  H 
springs  back  to  the  contact  screw,  and  the  cur- 
rent again  flows  in  the  primary  circuit  only  to  be 
interrupted  again  as  before.  In  this  way  the 
current  in  the  primary  coil  is  rapidly  started  and 
stopped  many  times  a  second,  and  this,  as  we 
know,  induces  corresponding  currents  in  the  sec- 
ondary which  appear  as  sparks  at  the  discharging 
points.  The  effect  of  the  apparatus  is  enhanced 
by  interpolating  a  "condenser"  C  C  in  the  pri- 
mary circuit.  A  condenser  is  a  form  of  Leyden 
jar,  suitable  for  current  electricity,  and  consists 
of  layers  of  tinfoil  separated  from  each  other  by 
sheets  of  paraffin  paper,  mica,  or  some  other  con- 
venient insulator,  and  alternate  foils  are  con- 
nected together.  The  wires  joining  each  set  of 
plates  are  the  poles  of  the  condenser,  and  when 
these  are  connected  in  the  circuit  of  a  current 
the  condenser  is  charged.  It  can  be  discharged 
by  joining  its  two  poles  with  a  wire,  and  letting 
the  two  opposite  electricities  on  its  plates  rush 
together.  Now,  the  sudden  discharge  of  the  con- 
denser C  C  through  the  primary  coil  P  C  enhances 
the  inductive  effect  of  the  current.  The  battery 
B,  here  shown  by,  the  conventional  symbol  "  I  |  " 
where  the  thick  dash  is  the  negative  and  the  thin 


THE   ELECTRICITY  OF   MAGNETISM.  63 

dash  the  positive  pole,  is  connected  between  the 
terminals  7\  T2,  and  a  commutator  or  pole-changer 
R,  turned  with  a  handle,  permits  the  direction  of 
the  current  to  be  reversed  at  will. 

Figure  36  represents  the  exterior  of  an  ordi- 
nary induction   coil  of   the   Ruhmkorff    pattern, 


FIG.  36.— The  Induction  Coil. 

with  its  two  coils,  one  over  the  other  C  its  com- 
mutator R,  and  its  sparkling  points  D±  Z>2,  the 
whole  being  mounted  on  a  mahogany  base,  which 
holds  the  condenser. 

The  intermittent,  or  rather  alternating,  cur- 
rents from  the  secondary  coil  are  often  applied 
to  the  body  in  certain  nervous  disorders.  When 
sent  through  glass  tubes  filled  with  rarefied  gases, 
sometimes  called  "  Geissler  tubes,"  they  elicit 
glows  of  many  colours,  vicing  in  beauty  with  the 
fleeting  tints  of  the  aurora  polaris,  which,  indeed, 
is  probably  a  similar  effect  of  electrical  discharges 
in  the  atmosphere. 

The  action  of  the  induction  is  reversible.  We 
can  not  only  send  a  current  of  low  "pressure" 
from  a  generator  of  weak  electromotive  force 
through  the  primaj^«rtt^psL  thus  excite  a  cur- 
rent of  high  pr0&jwffin  ftte  se&jpndary  coil,  but 


64  THE  STORY  OF  ELECTRICITY. 

we  can  send  a  current  of  high  pressure  through 
the  secondary  coil  and  provoke  a  current  of  low 
pressure  in  the  primary  coil.  The  transformer 
or  converter,  a  modified  induction  coil  used  in  dis- 
tributing electricity  to  electric  lamps  and  motors, 


can  not  only  transform  a 
low  pressure  current  into  a 
high,  but  -a  high  pressure 
current  into  a  low.  As  the 
high  pressure  currents  are  FIG.  37. 

best  able  to  overcome  the 
resistance  of  the  wire  conveying  them,  it  is  cus- 
tomary to  transmit  high  pressure  currents  from 
the  generator  to  the  distant  place  where  they 
are  wanted  by  means  of  small  wires,  and  there 
transform  them  into  currents  of  the  pressure 
required  to  light  the  lamps  or  drive  the  motors. 

We  come  now  to  another  consequence  of  Oer- 
sted's great  discovery,  which  is  doubtless  the 
most  important  of  all,  namely,  the  generation  of 
electricity  from  magnetism,  or,  as  it  is  usually 
called,  magneto-electric  induction.  In  the  year 
1831  the  illustrious  Michael  Faraday  further  suc- 
ceeded in  demonstrating  that  when  a  magnet  M 
is  thrust  into  a  hollow  coil  of  wire  C,  as  shown  in 
figure  37,  a  current  of  electricity  is  set  up  in  the 
coil  whilst  tbe  motion  lasts.  When  the  magnet  is 
withdrawn  again  another  current  is  induced  in 


THE   ELECTRICITY  OF  MAGNETISM.  65 

the  reverse  direction  to  the  first.  If  the  coil  be 
closed  through  a  small  galvanometer  G  the  move- 
ments of  the  needle  to  one  side  or  the  other  will 
indicate  these  temporary  currents.  It  follows 
from  the  principle  of  action  and  reaction  that  if 
the  magnet  is  kept  still  and  the  coil  thrust  over  it 
similar  currents  will  be  induced  in  the  coil.  All 
that  is  necessary  is  for  the  wires  to  cut  the  lines 
of  magnetic  force  around  the  magnet,  or,  in  other 
words,  the  lines  of  force  in  a  magnetic  field.  We 
have  seen  already  that  a  wire  conveying  a  current 
can  move  a  magnetic  pole,  and  we  are  therefore 
prepared  to  find  that  a  magnetic  pole  moved  near 
a  wire  can  excite  a  current  in  it. 

Figure  38  illustrates  the  conditions. of  this  re- 
markable effect,  where  N  and  S  are  two  magnetic 
poles  with  lines  of  force 
between  them,  and  Wis 
a  wire  crossing  these 
lines  at  right  angles, 

which  is  the  best  posi-  i~ — -j«— 4T~"~ 

tion.     If,  now,  this  wire         y|T///..V."''«  r.T.*V.'J".".'. '.]  S 

be  moved  so  as  to  sink  "• 

bodily  through  the  pa- 
per away  from  the  read-  ? 
er,  an    electric   current 
flowing  in  the  direction                   FIG.  38. 
of  the  arrow  will  be  in- 
duced  in    it.     If,  on    the  contrary,  the   wire  be 
moved  across  the  lines  of  force  towards  the  read- 
er, the  induced  current  will  flow. oppositely  to  the 
arrow.     Moreover,  if  the  poles  of  the  magnet  N 
and  S  exchange  places,  the  directions  of  the  in- 
duced currents  will  also  be  reversed.     This  is  the 
fundamental  principle  of  the  well-known  dynamo- 
electric  machine,  popularly  called  a  dynamo. 
5 


66 


THE  STORY  OF  ELECTRICITY. 


Again,  if  we  send  a  current  from  some  external 
source  through  the  wire  W  in  the  direction  of  the 
arrow,  the  wire  will  move  of  itself  across  the  lines 
of  force  away  from  the  reader,  that  is  to  say,  in 
the  direction  it  would  need  to  be  moved  in  order 
to  excite  such  a  current ;  and  if,  on  the  other 
hand,  the  current  be  sent  through  it  in  the  re- 
verse direction  to  the  arrow,  it  will  move  towards 
the  reader.  This  is  the  principle  of  the  equally 
well-known  electric  motor.  Figure  39  shows  a 
simple  method  of  remembering  these  directions. 

Let  the  right  hand  rest 
on  the  north  pole  of  a 
magnet  and  the  fore- 
finger be  extended  in 
the  direction  of  the 
lines  of  force,  then 
the  outstretched  thumb 
will  indicate  the  direc- 
tion in  which  the  wire 
or  conductor  moves 
and  the  bent  middle 
FIG.  39.  finger  the  direction  of 

the    current.        These 

three  digits,  as  will  be  noticed,  are  all  at 
right  angles  to  each  other,  and  this  relation  is 
the  best  for  inducing  the  strongest  current  in  a 
dynamo  or  the  most  energetic  movement  of  the 
conductor  in  an  electric  motor. 

Of  course  in  a  dynamo-electric  generator 
the  stronger  the  magnetic  field,  the  less  the 
resistance  of  the  conductor,  and  the  faster  it 
is  moved  across  the  lines  of  force,  that  is 
to  say,  the  more  lines  it  cuts  in  a  second  the 
stronger  is  the  current  produced.  Similarly 
in  an  electric  motor,  the  stronger  the  current 


THE   ELECTRICITY  OF   MAGNETISM.  67 

and  magnetic  field  the  faster  will  the  conductor 
move. 

The  most  convenient  motion  to  give  the  con- 
ductor in  practice  is  one  of  rotation,  and  hence 
the  dynamo  usually  consists  of  a  coil  or  series  of 
coils  of  insulated  wire  termed  the  "  armature," 
which  is  mounted  on  a  spindle  and  rapidly  ro- 
tated in  a  strong  magnetic  field  between  the 
poles  of  powerful  magnets.  Currents  are  gener- 
ated in  the  coils,  now  in  one  direction  then  in 
another,  as  they  revolve  or  cross  different  parts 
of  the  field ;  and,  by  means  of  a  device  termed  a 
commutator,  these  currents  can  be  collected  or 
sifted  at  will,  and  led  away  by  wires  to  an  electric 
lamp,  an  accumulator,  or  an  electric  motor,  as 
desired.  The  character  of  the  electricity  is  pre- 
cisely the  same  as  that  generated  in  the  voltaic 
battery. 

The  commutator  may  only  collect  the  currents 
as  they  are  generated,  and  supply  what  is  called 
an  alternating  current,  that  is  to  say,  a  current 
which  alternates  or  changes  its  direction  several 
hundred  times  a  second,  or  it  may  sift  the  cur- 
rents as  they  are  produced  and  supply  what  is 
termed  a  continuous  current,  that  is,  a  current 
always  in  the  same  direction,  like  that  of  a 
voltaic  battery.  Some  machines  are  made  to 
supply  alternating  currents,  others  continuous 
currents.  Either  class  of  current  will  do  for 
electric  lamps,  but  only  continuous  currents  are 
used  for  electo-plating,  or,  in  general,  for  electric 
motors. 

In  the  "  magneto-electric  "  machine  the  field 
magnets  are  simply  steel  bars  permanently  mag- 
netised, but  in  the  ordinary  dynamo  the  field 
magnets  are  electro-magnets  excited  to  a  high 


68 


THE  STORY  OF   ELECTRICITY. 


pitch  by  means  of  the  current  generated  in  the 
moving  conductor  or  armature.  In  the  "  series- 
wound  "  machine  the  whole  of  the  current  gener- 
ated in  the  armature  also  goes  through  the 
coils  of  the  field  magnets.  Such  a  machine  is 
sketched  in  figure  40,  where  A  is  the  armature, 
consisting  of  an  iron  core  surrounded  by  coils 
of  wire  and  rotating  in  the  field  of  a  powerful 
electro-magnet  NS  in  the  direction  of  the  arrows. 
For  the  sake  of  simplicity  only  twelve  coils  are 


FIG.  40. — A  Dynamo. 

represented.  They  are  all  in  circuit  one  with 
another,  and  a  wire  connects  the  ends  of  each 
coil  to  corresponding  metal  bars  on  the  commu- 
tator c.  These  bars  are  insulated  from  each  other 
on  the  spindle  X  of  the  armature.  Now,  as  each 
coil  passes  through  the  magnetic  field  in  turn, 
a  current  is  excited  in  it.  Each  coil  therefore 
resembles  an  individual  cell  of  a  voltaic  battery, 
connected  in  series.  The  current  is  drawn  off 
from  the  ring  by  two  copper  "  brushes  "  £,  V , 


THE   ELECTRICITY   OF   MAGNETISM.  69 

which  rub  upon  the  bars  of  the  commutator  at 
opposite  ends  of  a  diameter,  as  shown.  One 
brush  is  the  positive  pole  of  the  dynamo,  the 
other  is  the  negative,  and  the  current  will  flow 
through  any  wire  or  external  circuit  which  may 
be  connected  with  these,  whether  electric  lamps, 
motors,  accumulators,  electro-plating  baths,  or 
other  device.  The  small  arrows  show  the  move- 
ments of  the  current  throughout  the  machine, 
and  the  terminals  are  marked  (  +  )  positive  and 
(  — )  negative. 

It  will  be  observed  that  the  current  excited  in 
the  armature  also  flows  through  the  coils  of  the 
electro-magnets,  and  thus  keeps  up  their  strength. 
When  the  machine  is  first  started  the  current  is 
feeble,  because  the  field  of  the  magnets  in  which 
the  armature  revolves  is  merely  that  due  to  the 
dregs  or  "  residual  magnetism  "  left  in  the  soft 
iron  cores  of  the  magnet  since  the  last  time  the 
machine  was  used.  But  this  feeble  current  exalts 
the  strength  of  the  field-magnets,  producing  a 
stronger  field,  which  in  turn  excites  a  still 
stronger  current  in  the  armature,  and  this  pro- 
cess of  give  and  take  goes  on  until  the  full 
strength  or  u  saturation"  of  the  magnets  is  at- 
tained. 

Such  is  the  "  series "  dynamo,  of  which  the 
well-known  Gramme  machine  is  a  type.  Figure 
41  illustrates  this  machine  as  it  is  actually  made, 
A  being  the  armature  revolving  between  the 
poles  N S  of  the  field-magnets  MM,  M'  M' ,  on  a 
spindle  which  is  driven  by  means  of  a  belt  on 
the  pulley  P  from  a  separate  engine.  The  brushes 
b  bf  of  the  commutator  C  collect  the  current, 
which  in  this  case  is  continuous,  or  constant  in 
its  direction. 


70  THE   STORY   OF   ELECTRICITY. 

The  current  of  the  series  machine  varies  with 
the  resistance  of  the  external  or  working  circuit, 
because  that  is  included  in  the  circuit  of  the  field 
magnets  and  the  armature.  Thus,  if  we  vary  the 
number  of  electric  lamps  fed  by  the  machine,  we 
shall  vary  the  current  it  is  capable  of  yielding. 
With  arc  lamps  in  series,  by  adding  to  the  number 
in  circuit  we  increase  the  resistance  of  the  outer 


FIG.  41. 

circuit,  and  therefore  diminish  the  strength  of 
the  current  yielded  by  the  machine,  because  the 
current,  weakened  by  the  increase  of  resistance, 
fails  to  excite  the  field  magnets  as  strongly  as 
before.  On  the  other  hand,  with  glow  lamps 
arranged  in  parallel,  the  reverse  is  the  case,  and 
putting  more  lamps  in  circuit  increases  the  power 


THE  ELECTRICITY  OF   MAGNETISM. 


of  the  machine,  by  diminishing  the  resistance  of 
the  outer  circuit  in  providing  more  cross-cuts  for 
the  current.  This,  of  course,  is  a  drawback  to  the 
series  machine  in  places  where  the  number  of 
lamps  to  be  lighted  varies  from  time  to  time. 
In  the  "  shunt-wound  "  machine  the  field  magnets 
are  excited  by  diverting  a  small  portion  of  the 
main  current  from  the  armature  through  them, 
by  means  of  a  "  shunt  "  or  loop  circuit.  Thus  in 
figure  42  where  C  is  the 
commutator  and  b  b1  the 
brushes,  M  is  a  shunt 
circuit  through  the  mag- 
nets, and  E  is  the  exter- 
nal or  working  circuit  of 
the  machine. 

The  small  arrows  in- 
dicate the  directions  of 
the  currents.  With  this 
arrangement  the  addition 
of  more  glow  lamps  to 
the  external  circuit  E  di- 
minishes the  current,  be- 
cause the  portion  of  it  which  flows  through  the 
by-path  M9  and  excites  the  magnets,  is  less  now 
that  the  alternative  route  for  the  current  through 
E  is  of  lower  resistance  than  before.  When  fewer 
glow  lamps  are  in  the  external  circuit  E,  and  its 
resistance  therefore  higher,  the  current  in  the  shunt 
circuit  M  is  greater  than  before,  the  magnets  be- 
come stronger,  and  the  electromotive  force  of  the 
armature  is  increased.  The  Edison  machine  is  of 
this  type,  and  is  illustrated  in  figure  43,  where 
MM1  are  the  field  magnets  with  their  poles  N  S, 
between  which  the  armature  A  is  revolved  by 
mea.ns  of  the  bejt  B,  and  a  pulley  seen  behind. 


\J\J\f\f\T\J\f\) 

E 
FIG.  42. 


72  THE   STORY  OF   ELECTRICITY. 

The  leading  wires  W  W  convey  the  current  from 
the  brushes  of  the  commutator  to  the  external 


K' 


FIG.  43. 

circuit.  In  this  machine  the  conductors  of  the 
armature  are  not  coils  of  wire,  but  separate  bars 
of  copper. 

In  shunt  machines  the  variation  of  current  due 


THE   ELECTRICITY  OF   MAGNETISM.  73 

to  a  varying  number  of  lamps  in  use  occasions  a 
rise  and  fall  in  the  brightness  of  the  lamps  which 
is  undesirable,  and  hence  a  third  class  of  dynamo 
has  been  devised,  which  combines  the  principles 
of  both  the  series  and  shunt  machines.  This  is 
the  "compound-wound"  machine,  in  which  the 
magnets  are  wound  partly  in  shunt  and  partly  in 
series  with  the  armature,  in  such  a  manner  that 
the  strength  of  the  field-magnets  and  the  electro- 
motive force  of  the  current  do  not  vary  much, 
whatever  be  the  number  of  lamps  in  circuit.  In 
alternate  current  machines  the  electromotive  force 
keeps  constant,  as  the  field-magnets  are  excited 
by  a  separate  machine,  giving  a  continuous  cur- 
rent. 

We  have  already  seen  that  the  action  of  the 
dynamo  is  reversible,  and  that  just  as  a  wire 
moved  across  a  magnetic  field  supplies  an  electric 
current,  so  a  wire  at  rest,  but  conducting  a  cur- 
rent across  a  magnetic  field,  will  move.  The 
electric  motor  is  therefore  essentially  a  dynamo, 
which  on  being  traversed  by  an  electric  current 
from  an  external  source  puts  itself  in  motion. 
Thus,  if  a  current  be  sent  through  the  armature 
of  the  Gramme  machine,  shown  in  figure  41,  the 
armature  will  revolve,  and  the  spindle,  by  means 
of  a  belt  on  the  pulley  P,  can  communicate  its 
energy  to  another  machine. 

Hence  the  electric  motor  can  be  employed  to 
work  lathes,  hoists,  lifts,  drive  the  screws  of  boats 
or  the  wheels  of  carriages,  and  for  many  other 
purposes.  There  are  numerous  types  of  electric 
motor  as  of  the  dynamo  in  use,  but  they  are  all 
modifications  of  the  simple  continuous  or  alter- 
nating current  dynamo. 

Obviously,    since    mechanical    power   can    be 


74  THE   STORY   OF   ELECTRICITY. 

converted  into  electricity  by  the  dynamo,  and  re- 
converted into  mechanical  power  by  the  motor,  it 
is  sufficient  to  connect  a  dynamo  and  motor  to- 
gether by  insulated  wire  in  order  to  transmit  me- 
chanical power,  whether  it  be  derived  from  wind, 
water,  or  fuel,  to  any  reasonable  distance. 


CHAPTER   V. 

ELECTROLYSIS. 

HAVING  seen  how  electricity  can  be  generated 
and  stored  in  considerable  quantity,  let  us  now 
turn  to  its  practical  uses.  Of  these  by  far  the 
most  important  are  based  on  its  property  of  de- 
veloping light  and  heat  as  in  the  electric  spark, 
chemical  action  as  in  the  voltameter,  and  magnet- 
ism as  in  the  electromagnet. 

The  words  "  current,"  "  pressure,"  and  so  on 
point  to  a  certain  analogy  between  electricity  and 
water,  which  helps  the  imagination  to  figure  what 
can  neither  be  seen  nor  handled,  though  it  must 
not  be  traced  too  far.  Water,  for  example,  runs 
by  the  force  of  gravity  from  a  place  of  higher  to 
a  place  of  lower  level.  The  pressure  of  the 
stream  is  greater  the  more  the  difference  of  level 
or  "  head  of  water."  The  strength  of  the  current 
or  quantity  of  water  flowing  per  second  is  greater 
the  higher  the  pressure,  and  the  less  the  resist- 
ance of  its  channel.  The  power  of  the  water  or 
its  rate  of  doing  mechanical  work  is  greater  the 
higher  the  pressure  and  the  stronger  the  current. 

So,  too,  electricity  flows  by  the  electromotive 
force  from  a  place  of  higher  to  a  place  pf  lower 


ELECTROLYSIS.  75 

electric  level  or  potential.  The  electric  pressure 
is  greater  the  more  the  difference  of  potential  or 
electromotive  force.  The  strength  of  the  electric 
current  or  quantity  of  electricity  flowing  per  sec- 
ond is  greater  the  higher  the  pressure  or  electro- 
motive force  and  the  less  the  resistance  of  the 
circuit.  The  power  of  the  electricity  or  its  rate 
of  doing  work  is  greater  the  higher  the  electro- 
motive force  and  the  stronger  the  current. 

It  follows  that  a  small  quantity  of  water  or 
electricity  at  a  high  pressure  will  give  us  the 
same  amount  of  energy  as  a  large  quantity  at  a 
low  pressure,  and  our  choice  of  one  or  the  other 
will  depend  on  the  purpose  we  have  in  view.  As 
a  rule,  however,  a  large  current  at  a  compara- 
tively low  or  moderate  pressure  is  found  the  more 
convenient  in  practice. 

The  electricity  of  friction  belongs  to  the 
former  category,  and  the  electricity  of  chemistry, 
heat,  and  magnetism  to  the  latter.  The  spark  of 
a  frictional  or  influence  machine  can  be  compared 
to  a  highland  cataract  of  lofty  height  but  small 
volume,  which  is  more  picturesque  than  useful, 
and  the  current  from  a  voltaic  battery,  a  thermo- 
pile, or  a  dynamo  to  a  lowland  river  which  can 
be  dammed  to  turn  a  mill.  It  is  the  difference 
between  a  skittish  gelding  and  a  tame  cart- 
horse. 

Not  the  spark  from  an  induction  coil  or  Ley- 
den  jar,  but  a  strong  and  steady  current  at  a  low 
pressure,  is  adapted  for  electrolysis  or  electro-de- 
position, and  hence  the  voltaic  battery  or  a  special 
form  of  dynamo  is  usually  employed  in  this  work. 
A  flash  of  lightning  is  the  very  symbol  of  terrific 
power,  and  yet,  according  to  the  illustrious  Fara- 
day, it  contains  a  smaller  amount  of  electricity 


76  THE   STORY   OF   ELECTRICITY. 

than  the  feeble  current  required  to  decompose  a 
single  drop  of  rain. 

In  our  simile  of  the  mill  dam  and  the  battery 
or  dynamo,  the  dam  corresponds  to  the  positive 
pole  and  the  river  or  sea  below  the  mill  to  the 
negative  pole.  The  mill-race  will  stand  for  the 
wire  joining  the  poles,  that  is  to  say,  the  external 
circuit,  and  the  mill-wheel  for  the  work  to  be  done 
in  the  circuit,  whether  it  be  a  chemical  for  decom- 
position, a  telegraph  instrument,  an  electric  lamp, 
or  any  other  appliance.  As  the  current  in  the 
race  depends  on  the  "  head  of  water,"  or  differ- 
ence of  level  between  the  dam  and  the  sea  as  well 
as  on  the  resistance  of  the  channel,  so  the  cur- 
rent in  the  circuit  depends  on  the  "  electromotive 
force,"  or  difference  of  potential  between  the  posi- 
tive and  negative  poles,  as  well  as  on  the  resist- 
ance of  the  circuit.  The  relation  between  these 
is  expressed  by  the  well-known  law  of  Ohm,  which 
runs  :  A  current  of  electricity  is  directly  proportional 
to  the  electromotive  force  and  inversely  proportional 
to  the  resistance  of  the  circuit. 

In  practice  electricity  is  measured  by  various 
units  or  standards  named  after  celebrated  elec- 
tricians. Thus  the  unit  of  quantity  is  the  coulomb, 
the  unit  of  current  or  quantity  flowing  per  second 
is  the  ampere,  the  unit  of  electromotive  force  is 
the  volt,  and  the  unit  of  resistance  is  the  ohm. 

The  quantity  of  water  or  any  other  "  electro- 
lyte "  decomposed  by  electricity  is  proportional 
to  the  strength  of  the  current.  One  ampere  de- , 
composes  .00009324  gramme  of  water  per  second, 
liberating  .000010384  gramme  of  hydrogen  and 
.00008286  gramme  of  oxygen. 

The  quantity  in  grammes  of  any  other  chemi- 
cal element  or  ion  which  is  liberated  from  an  elec- 


ELECTROLYSIS.  77 

trolyte  or  body  capable  of  electro-chemical  de- 
composition in  a  second  by  a  current  of  one 
ampere  is  given  by  what  is  called  the  electro- 
chemical equivalent  of  the  ion.  This  is  found  by 
multiplying  its  ordinary  chemical  equivalent  or 
combining  weight  by  .000010384,  which  is  the  elec- 
tro-chemical equivalent  of  hydrogen.  Thus  the 
weight  of  metal  deposited  from  a  solution  of  any 
of  its  salts  by  a  current  of  so  many  amperes  in  so 
many  seconds  is  equal  to  the  number  of  amperes 
multiplied  by  the  number  of  seconds,  and  by  the 
electro-chemical  equivalent  of  the  metal. 

The  deposition  of  a  metal  from  a  solution  of 
its  salt  is  very  easily  shown  in  the  case  of  cop- 
per. In  fact,  we  have  already  seen  that  in  the 
Daniell  cell  the  current  decomposes  a  solution  of 
sulphate  of  copper  and  deposits  the  pure  metal 
on  the  copper  plate.  If  we  simply  make  a  solu- 
tion of  blue  vitriol  in  a  glass  beaker  and  dip  the 
wires  from  a  voltaic  cell  into  it,  we  shall  find  the 
wire  from  the  negative  pole  become  freshly  coated 
with  particles  of  new  copper.  The  sulphate  has 
been  broken  up,  and  the  liberated  metal,  being 
positive,  gathers  on  the  negative  electrode. 
Moreover,  if  we  examine  the  positive  electrode 
we  shall  find  it  slightly  eaten  away,  because  the 
sulphuric  acid  set  free  from  the  sulphate  has 
combined  with  the  particles  of  that  wire  to  make 
new  sulphate.  Thus  the  copper  is  deposited  on 
one  electrode,  namely,  the  cathode,  by  which  the 
current  leaves  the  bath,  and  at  the  expense  of 
the  other  electrode,  that  is  to  say,  the  anode,  by 
which  the  current  enters  the  bath. 

The  fact  that  the  weight  of  metal  deposited  in 
this  way  from  its  salts  is  proportional  to  the 
current,  has  been  utilised  for  measuring  the 


78  THE  STORY  OF   ELECTRICITY, 

strength  of  currents  with  a  fine  degree  of  ac, 
curacy.  If,  for  example,  the  tubes  of  the  vol- 
tameter described  on  page  38  were  graduated, 
the  volume  of  gas  evolved  would  be  a  measure 
of  the  current.  Usually,  however,  it  is  the 
weight  of  silver  or  copper  deposited  from  their 
salts  in  a  certain  time  which  gives  the  current  in 
amperes. 

Electro-plating  is  the  principal  application  of 
this  chemical  process.  In  1805  Brugnatelli  took 
a  silver  medal  and  coated  it  with  gold  by  making 
it  the  cathode  in  a  solution  of  a  salt  of  gold,  and 
using  a  plate  of  gold  for  the  anode.  The  shops 
of  our  jewellers  are  now  bright  with  teapots,  salt 
cellars,  spoons,  and  other  articles  of  the  table 
made  of  inferior  metals,  but  beautified  and  pre- 
served from  rust  in  this  way. 

Figure  44  illustrates  an  electro-plating  bath 


FIG.  44. 

in  which  a  number  of  spoons  are  being  plated. 
A  portion  of  the  vat  V  is  cut  away  to  show  the 
interior,  which  contains  a  solution  *Sof  the  double 
cyanide  of  gold  and  potassium  when  gold  is  to  be 


ELECTROLYSIS.  79 

laid,  and  the  double  cyanide  of  silver  and  potas- 
sium when  silver  is  to  be  deposited.  The  elec- 
trodes are  hung  from  metal  rods,  the  anode  A 
being  a  plate  of  gold  or  silver  G,  as  the  case  may 
be,  and  the  cathode  C  the  spoons  in  question. 
When  the  current  of  the  battery  or  dynamo 
passes  through  the  bath  from  the  anode  to  the 
cathode,  gold  or  silver  is  deposited  on  the  spoons, 
and  the  bath  recuperates  its  strength  by  consum- 
ing the  gold  or  silver  plate. 

Enormous  quantities  of  copper  are  now  de- 
posited in  a  similar  way,  sulphate  of  copper  being 
the  solution  and  a  copper  plate  the  anode.  Large 
articles  of  iron,  such  as  the  parts  of  ordnance,  are 
sometimes  copper-plated  to  preserve  them  from 
the  action  of  the  atmosphere.  Seamless  copper 
pipes  for  conveying  steam,  and  wires  of  pure  cop- 
per for  conducting  electricity,  are  also  deposited, 
and  it  is  not  unlikely  that  the  kettle  of  the  future 
will  be  made  by  electrolysis. 

Nickel-plating  is  another  extensive  branch  of 
the  industry,  the  white  nickel  forming  a  cloak 
for  metals  more  subject  to  corrosion.  Nickel  is 
found  to  deposit  best  from  a  solution  of  the 
double  sulphate  of  nickel  and  ammonia.  Alu- 
minium, however,  has  not  yet  been  successfully 
deposited  by  electricity. 

In  1836  De  la  Rue  observed  that  copper  laid 
in  this  manner  on  another  surface  took  on  its 
under  side  an  accurate  impression  of  that  surface, 
even  to  the  scratches  on  it,  and  three  years  later 
Jacobi,  of  St.  Petersburg,  and  Jordan,  of  London, 
applied  the  method  to  making  copies  or  replicas 
of  medals  and  woodcuts.  Even  non-metallic  sur- 
faces could  be  reproduced  in  copper  by  taking  a 
cast  of  them  in  wax  and  lining  the  mould  with 


8o  THE   STORY  OF  ELECTRICITY. 

fine  plumbago,  which,  being  a  conductor,  served 
as  a  cathode  to  receive  the  layer  of  metal.  It  is 
by  the  process  of  electrotyping  or  galvano-plastics 
that  the  copper  faces  for  printing  woodcuts  are 
prepared,  and  copies  made  of  seals  or  medals. 

Natural  objects,  such  as  flowers,  ferns,  leaves, 
feathers,  insects,  and  lizards,  can  be  prettily 
coated  with  bronze  or  copper,  not  to  speak  of 
gold  and  silver,  by  a  similar  process.  They  are 
too  delicate  to  be  coated  with  black  lead  in  order 
to  receive  the  skin  of  metal,  but  they  can  be 
dipped  in  solutions,  leaving  a  film  which  can  be 
reduced  to  gold  or  silver.  For  instance,  they  may 
be  soaked  in  an  alcoholic  solution  of  nitrate  of 
silver,  made  by  shaking  2  parts  of  the  crystals  in 
100  parts  of  alcohol  in  a  stoppered  bottle.  When 
dry,  the  object  should  be  suspended  under  a  glass 
shade  and  exposed  to  a  stream  of  sulphuretted 
hydrogen  gas ;  or  it  may  be  immersed  in  a  solu- 
tion of  i  part  of  phosphorus  in  15  parts  of  bisul- 
phide of  carbon,  i  part  of  bees-wax,  i  part  of 
spirits  of  turpentine,  i  part  of  asphaltum,  and  */8 
part  of  caoutchouc  dissolved  in  bisulphide  of  car- 
bon. This  leaves  a  superficial  film  which  is 
metallised  by  dipping  in  a  solution  of  20  grains 
of  nitrate  of  silver  to  a  pint  of  water.  On  this 
metallic  film  a  thicker  layer  of  gold  and  silver  in 
different  shades  can  be  deposited  by  the  current, 
and  the  silver  surface  may  also  be  "  oxidised " 
by  washing  it  in  a  weak  solution  of  platinum 
chloride. 

Electrolysis  is  also  used  to  some  extent  in 
reducing  metals  from  their  ores,  in  bleaching 
fibre,  in  manufacturing  hydrogen  and  oxygen 
from  water,  and  in  the  chemical  treatment  of 
sewage. 


THE  TELEGRAPH  AND  TELEPHONE.     8l 

CHAPTER  VI. 

THE  TELEGRAPH  AND  TELEPHONE. 

LIKE  the  "philosopher's  stone,"  the  "elixir  of 
youth,"  and  "perpetual  motion,"  the  telegraph 
was  long  a  dream  of  the  imagination.  In  the 
sixteenth  century,  if  not  before,  it  was  believed 
that  two  magnetic  needles  could  be  made  sym- 
pathetic, so  that  when  one  was  moved  the  other 
would  likewise  move,  however  far  apart  they 
were,  and  thus  enable  two  distant  friends  to  com- 
municate their  minds  to  one  another. 

The  idea  was  prophetic,  although  the  means 
of  giving  effect  to  it  were  mistaken.  It  became 
practicable,  however,  when  Oersted  discovered 
that  a  magnetic  needle  could  be  swung  to  one 
side  or  the  other  by  an  electric  current  passing 
near  it. 

The  illustrious  Laplace  was  the  first  to  suggest 
a  telegraph  on  this  principle.  A  wire  connecting 
the  two  poles  of  a  battery  is  traversed,  as  we 
know,  by  an  electric  current,  which  makes  the 
round  of  the  circuit,  and  only  flows  when  that 
circuit  is  complete.  However  long  the  wire  may 
be,  however  far  it  may  run  between  the  poles, 
the  current  will  follow  all  its  windings,  and  finish 
its  course  from  pole  to  pole  of  the  battery.  You 
may  lead  the  wire  across  the  ocean  and  back,  or 
round  the  world  if  you  will,  and  the  current  will 
travel  through  it. 

The  moment  you  break  the  wire  or  circuit, 
however,  the  current  will  stop.  By  its  electro- 
motive force  it  can  overcome  the  resistance  of 
the  many  miles  of  conductor  ;  but  unless  it  be 
6 


82  THE   STORY  OF  ELECTRICITY. 

unusually  strong  it  cannot  leap  across  even  a 
minute  gap  of  air,  which  is  one  of  the  best  in- 
sulators. 

If,  then,  we  have  a  simple  device  easily  manip- 
ulated by  which  we  can  interrupt  the  circuit  of 
the  battery,  in  accordance  with  a  given  code,  we 
shall  be  able  to  send  a  series  of  currents  through 
the  wire  and  make  sensible  signals  wherever  we 
choose.  These  signs  can  be  produced  by  the 
deviation  of  a  magnetic  needle,  as  Laplace  pointed 
out,  or  by  causing  an  electro-magnet  to  attract 
soft  iron,  or  by  chemical  decomposition,  or  any 
other  sensible  effect  of  the  current. 

Ampere  developed  the  idea  of  Laplace  into  a 
definite  plan,  and  in  1830  or  thereabout  Ritchie, 
in  London,  and  Baron  Schilling,  in  St.  Petersburg, 
exhibited  experimental  models.  In  1833  and 
afterwards  Professors  Gauss  and  Weber  installed 
a  private  telegraph  between  the  observatory  and 
the  physical  cabinet  of  the  University  of  Got- 
tingen.'  Moreover,  in  1836  William  Fothergill 
Cooke,  a  retired  surgeon  of  the  Madras  army, 
attending  lectures  on  anatomy  at  the  University 
of  Heidelberg,  saw  an  experimental  telegraph  of 
Professor  Moncke,  which  turned  all  his  thoughts 
to  the  subject.  On  returning  to  London  he  made 
the  acquaintance  of  Professor  Wheatstone,  of 
King's  College,  who  was  also  experimenting  in 
this  direction,  and  in  1836  they  took  out  a 
patent  for  a  needle  telegraph.  It  was  tried 
successfully  between  the  Euston  terminus  and 
the  Camden  Town  station  of  the  London  and 
North-Western  Railway  on  the  evening  of  July 
25th,  1837,  in  presence  of  Mr.  Robert  Stephen- 
son,  and  other  eminent  engineers.  Wheatstone,^ 
sitting  in  a  small  room  near  the  booking-office  at 


THE  TELEGRAPH  AND  TELEPHONE.     83 

Euston,  sent  the  first  message  to  Cooke  at  Cam- 
den  Town,  who  at  once  replied.  "  Never,"  said 
Wheatstone,  "did  I  feel  such  a  tumultuous  sensa- 
tion before,  as  when,  all  alone  in  the  still  room,  I 
heard  the  needles  click,  and  as  I  spelled  the 
words  I  felt  all  the  magnitude  of  the  invention 
pronounced  to  be  practicable  without  cavil  or 
dispute." 

The  importance  of  the  telegraph  in  working 
railways  was  manifest,  and  yet  the  directors  of 
the  company  were  so  purblind  as  to  order  the 
removal  of  the  apparatus,  and  it  was  not  until 
two  years  later  that  the  Great  Western  Railway 
Company  adopted  it  on  their  line  from  Padding- 
ton  to  West  Drayton,  and  subsequently  to  Slough. 
This  was  the  first  telegraph  for  public  use,  not 
merely  in  England,  but  the  world.  The  charge 
for  a  message  was  only  a  shilling,  nevertheless 
few  persons  availed  themselves  of  the  new  inven- 
tion, and  it  was  not  until  its  fame  was  spread 
abroad  by  the  clever  capture  of  a  murderer 
named  Tawell  that  it  began  to  prosper.  Tawell 
had  killed  a  woman  at  Slough,  and  on  leaving  his 
victim  took  the  train  for  Paddington.  The  police, 
apprised  of  the  murder,  telegraphed  a  description 
of  him  to  London.  The  original  "  five  needle 
instrument,"  now  in  the  museum  of  the  Post 
Office,  had  a  dial  in  the  shape  of  a  diamond,  on 
which  were  marked  the  letters  of  the  alphabet, 
and  each  letter  of  a  word  was  pointed  out  by  the 
movements  of  a  pair  of  needles.  The  dial  had 
no  letter  "  q,"  and  as  the  man  was  described  as 
a  quaker  the  word  was  sent  "  kwaker."  When 
the  train  arrived  at  Paddington  he  was  shadowed 
by  detectives,  and  to  his  utter  astonishment  was 
quietly  arrested  in  a  tavern  near  Cannon  Street. 


84  THE   STORY  OF  ELECTRICITY. 

In  Cooke  and  Wheatstone's  early  telegraph 
the  wire  travelled  the  whole  round  of  the  circuit, 
but  it  was  soon  found  that  a  "  return  "  wire  in 
the  circuit  was  unnecessary,  since  the  earth  itself 
could  take  the  place  of  it.  One  wire  from  the 
sending  station  to  the  receiving  station  was 
sufficient,  provided  the  apparatus  at  each  end 
were  properly  connected  to  the  ground.  This 
use  of  the  earth  not  only  saved  the  expense  of  a 
return  wire,  but  diminished  the  resistance  of  the 
circuit,  because  the  earth  offered  practically  no 
resistance. 

Figure  45  is  a  diagram  of  the  connections  in  a 


e 


FIG.  45. 


simple  telegraph  circuit.  At  each  of  the  stations 
there  is  a  battery  B  B1  ,  an  interrupter  or  sending 
key  K  K'  to  make  and  break  the  continuity  of  the 
circuit,  a  receiving  instrument  £  £'  to  indicate 
the  signal  currents  by  their  sensible  effects,  and 
connections  with  ground  or  "  earth  plates  "  E  E! 
to  engage  the  earth  as  a  return  wire.  These 
are  usually  copper  plates  buried  in  the  moist 
subsoil  or  the  water  pipes  of  a  city.  The  line 
wire  is  commonly  of  iron  supported  on  poles, 
but  insulated  from  them  by  earthenware  "cups" 
or  insulators. 

At  the  station  on  the  left  the  key  is  in  the  act 


THE  TELEGRAPH  AND  TELEPHONE.     85 

of  sending  a  message,  and  at  the  post  on  the  right 
it  is  conformably  in  the  position  for  receiving  the 
message.  The  key  is  so  constructed  that  when  it 
is  at  rest  it  puts  the  line  in  connection  with  the 
earth  through  the  receiving  instrument  and  the 
earth  plate. 

The  key  K  consists  essentially  of  a  spring- 
lever,  with  two  platinum  contacts,  so  placed  that 
when  the  lever  is  pressed  down  by  the  hand  of 
the  telegraphist  it  breaks  contact  with  the  re- 
ceiver R,  and  puts  the  line-wire  L  in  connection 
with  the  earth  E  through  the  battery  B,  as  shown 
on  the  left.  A  current  then  flows  into  the  line 
and  traverses  the  receiver  R'  at  the  distant  sta- 
tion, returning  or  seeming  to  return  to  the  send- 
ing battery  by  way  of  the  earth  plate  E'  on  the 
right  and  the  intermediate  ground. 

The  duration  of  the  current  is  at  the  will  of 
the  operator  who  works  the  sending-key,  and  it  is 
plain  that  signals  can  be  made  by  currents  of 
various  lengths.  In  the  "  Morse  code  "  of  sig- 
nals, which  is  now  universal,  only  two  lengths  of 
current  are  employed — namely,  a  short,  momen- 
tary pulse,  produced  by  instant  contact  of  the 
key,  and  a  jet  given  by  a  contact  about  three 
times  longer.  These  two  signals  are  called 
"  dot  "  and  "  dash,"  and  the  code  is  merely  a  suit- 
able combination  of  them  to  signify  the  several 
letters  of  the  alphabet.  Thus  e,  the  commonest 
letter  in  English,  is  telegraphed  by  a  single  u  dot," 
and  the  letter  /  by  a  single  "  dash,"  while  the  let- 
ter a  is  indicated  by  a  "  dot  "  followed  after  a  brief 
interval  or  "  space  "  by  a  dash. 

Obviously,  if  two  kinds  of  current  are  used, 
that  is  to  say,  if  the  poles  of  the  battery  are 
reversed  by  the  sending-key,  and  the  direction 


86  THE  STORY  OF   ELECTRICITY. 

of  the  current  is  consequently  reversed  in  the 
circuit,  there  is  no  need  to  alter  the  length  of  the 
signal  currents,  because  a  momentary  current 
sent  in  one  direction  will  stand  for  a  "dot  "  and 
in  the  other  direction  for  a  "  dash."  As  a  matter 
of  fact,  the  code  is  used  in  both  ways,  according 
to  the  nature  of  the  line  and  receiving  instru- 
ment. On  submarine  cables  and  with  needle 
and  "  mirror  "  instruments,  the  signals  are  made 
by  reversing  currents  of  equal  duration,  but  on 
land  lines  worked  by  "  Morse  "  instruments  and 
"  sounders,"  they  are  produced  by  short  and  long 
currents. 

The  Morse  code  is  also  used  in  the  army  for 
signalling  by  waving  flags  or  flashing  lights,  and 
may  also  be  serviceable  in  private  life.  Tele- 
graph clerks  have  been  known  to  "  speak  "  with 
each  other  in  company  by  winking  the  right 
and  left  eye,  or  tapping  with  their  teaspoon  on 
a  cup  and  saucer.  Any  two  distinct  signs,  how- 
ever made,  can  be  employed  as  a  telegraph  by 
means  of  the  Morse  code,  which  runs  as  shown 
in  figure  46. 

The  receiving  instruments  RIP  may  consist 
of  a  magnetic  needle  pivotted  on  its  centre  and 
surrounded  by  a  coil  of  wire,  through  which  the 
current  passes  and  deflects  the  needle  to  one  side 
or  the  other,  according  to  the  direction  in  which 
it  flows.  Such  was  the  pioneer  instrument  of 
Cooke  and  Wheatstone,  which  is  still  employed 
in  England  in  a  simplified  form  as  the  "  single  " 
and  "  double  "  needle-instrument  on  some  of  the 
local  lines  and  in  railway  telegraphs.  The  signals 
are  made  by  sending  momentary  currents  in  oppo- 
site directions  by  a  "  double  current  "  key,  which 
(unlike  the  key  K  in  figure  45)  reverses  the  poles 


THE  TELEGRAPH  AND  TELEPHONE. 


Needle  and 
Morse  Instrument.          Mirror 

Instrument. 


A 

Mae) 
B 
C 
D 
E 
F 
6 
H 
I 


Morse  Instrument. 


Needle  and 
Mirror 

Instrument 


J 

J 

yy 

K 

Axx 

L 

AA 

M 

Av 

N 

X 

0 

/A 

P 

\\\x 

Q 

\\ 

R 

(oe) 


S        --• 

v\\ 

1   

T        — 

/ 

U        ..— 

xx/ 

2    „___.. 

ti  (ue)  ^» 

xx// 

0       -  .  -  — 

V        

xxv/ 

5 

\V  .      

y/ 

X        

A/ 

o    —  --  - 

Y         

A// 

*       "™"  "™"  " 

z      

/A 

Q      -      —  ~ 

0    —  

J// 

/J 


//A 
s/A 

//y 


y/// 

VS/// 

w// 

\\\v/ 
\\\\\ 
/v\\\ 
/Axx 

///* 


FIG.  46. — Morse  Signal  Alphabet. 

of  the  battery,  in  putting  the  line  to  one  or  the 
other,  and  thus  making  the  "  dot  "  signal  with 
the  "  positive  "  and  the  "  dash  "  signal  with  the 
negative  pole.  It  follows  that  if  the  "  dot  "  is 
indicated  by  a  throw  of  the  needle  to  the  right 
side,  a  "  dash  "  will  be  given  by  a  throw  to  the 
left. 

Most  of  the  telegraph    instruments    for  land 
lines  are  based  on   the  principle  of  the  electro- 


88 


THE  STORY  OF   ELECTRICITY. 


magnet.  We  have  already  seen  (page  59)  how 
Ampere  found  that  a  spiral  of  wire  with  a  cur- 
rent flowing  in  it  behaved  like  a  magnet  and  was 
able  to  suck  a  piece  of  soft  iron  into  it.  If  the 
iron  is  allowed  to  remain  there  as  a  core,  the 
combination  of  coil  and  core  becomes  an  electro- 
magnet, that  is  to  say,  a  magnet  which  is  only  a 
magnet  so  long  as  the  current  passes.  Figure 
47  represents  a  simple  u  horse-shoe "  electro- 
A  magnet  as  invented  by 

Sturgeon,  A  U-shaped 
core  of  soft  iron  is 
wound  with  insulated 
wire  W,  and  when  a 
current  is  sent  through 
the  wire,  the  core  is 
found  to  become  mag- 
netic with  a  "  north  " 
pole  in  one  end  and  a 
"south"  pole  in  the 
other.  These  poles 
are  therefore  able  to 


U 


FIG.  47. 
A  Simple  Electro  Magnet. 


attract  a  separate  piece 

of  soft  iron  or  armature  A.  When  the  cur- 
rent is  stopped,  however,  the  core  ceases  to  be 
a  magnet  and  the  armature  drops  away.  In  prac- 
tice the  electromagnet  usually  takes  the  form 
shown  in  figure  48,  where  the  poles  are  two  bob- 
bins or  solenoids  of  wire  S  having  straight  cores 
of  iron  which  are  united  by  an  iron  bar^,  and  A 
is  the  armature. 

Such  an  electromagnet  is  a  more  powerful 
device  than  a  swinging  needle,  and  better  able  to 
actuate  a  mechanism.  It  became  the  foundation 
of  the  recording  instrument  of  Samuel  Morse,  the 
father  of  the  telegraph  in  America.  The  Morse, 


THE  TELEGRAPH  AND  TELEPHONE. 


89 


or,  rather,  Morse  and  Vail  instrument,  actually 
marks  the  signals  in  "  dots  "  and  "  dashes  "  on  a 
ribbon  of  moving  paper.  Figure  49  represents 
the  Morse  instrument,  in  which  an  electromagnet 
M  attracts  an  iron  armature  A  when  a  current 
passes  through  its  bobbins,  and  by  means  of  a 
lever  L  connected  with  the  armature  raises  the 
edge  of  a  small  disc  out 
of  an  ink-pot  /  against 
the  surface  of  a  travelling 
slip  of  paper  P,  and  marks 
a  dot  or  dash  upon  it  as 
the  case  may  be.  The 
rest  of  the  apparatus  con- 
sists of  details  and  ac- 
cessories for  its  action 
and  adjustment,  together 
with  the  sending-key  K,  which  is  used  in  asking 
for  repetitions  of  the  words,  if  necessary. 

A    permanent    record   of    the    message    is   of 


FIG.  48.— Electro  Magnet. 


FIG.  49. 


course  convenient,  nevertheless  the  operators 
prefer  to  u  read  "  the  signals  by  the  ear,  rather 
than  the  eye,  and,  to  the  annoyance  of  Morse, 


90  THE   STORY   OF   ELECTRICITY. 

would  listen  to  the  click  of  the  marking  disc 
rather  than  decipher  the  marks  on  the  paper. 
Consequently  Alfred  Vail,  the  collaborator  of 
Morse,  who  really  invented  the  Morse  code,  pro- 
duced a  modification  of  the  recording  instrument 
working  solely  for  the  ear.  The  "  sounder,"  as 
it  is  called,  has  largely  driven  the  "  printer " 
from  the  field.  This  neat  little  instrument  is 
shown  in  figure  50,  where  M  is  the  electromag- 
net, and  A  is  the  armature  which  chatters  up  and 


FIG.  50. 

down  between  two  metal  stops,  as  the  current  is 
made  and  broken  by  the  sending-key,  and  the 
operator  listening  to  the  sounds  interprets  the 
message  letter  by  letter  and  word  by  word. 

The  motion  of  the  armature  in  both  of  these 
instruments  takes  a  sensible  time,  but  Alexander 
Bain,  of  Thurso,  by  trade  a  watchmaker,  and  by 
nature  a  genius,  invented  a  chemical  telegraph 
which  was  capable  of  a  prodigious  activity.  The 
instrument  of  Bain  resembled  the  Morse  in  mark- 
ing the  signals  on  a  tape  of  moving  paper,  but 


THK  TELEGRAPH  AND  TELEPHONE.     91 

this  was  done  by  electrolysis  or  electro-chemical 
decomposition.  The  paper  was  soaked  in  a  solu- 
tion of  iodide  of  potassium  in  starch  and  water, 
and  the  signal  currents  were  passed  through  it 
by  a  marking  stylus  or  pencil  of  iron.  The  elec- 
tricity decomposed  the  solution  in  its  passage  and 
left  a  blue  stain  on  the  paper,  which  corresponded 
to  the  dot  and  dash  of  the  Morse  apparatus. 
The  Bain  telegraph  can  record  over  1000  words 
a  minute  as  against  40  to  50  by  the  Morse  or 
sounder,  nevertheless  it  has  fallen  into  disuse, 
perhaps  because  the  solution  was  troublesome. 

It  is  stated  that  a  certain  blind  operator  could 
read  the  signals  by  the  smell  of  the  chemical  ac- 
tion ;  and  we  can  well  believe  it.  In  fact,  the 
telegraph  appeals  to  every  sense,  for  a  deaf  clerk 
can  feel  the  movements  of  a  sounder,  and  the 
signals  of  the  current  can  be  told  without  any 
instrument  by  the  mere  taste  of  the  wires  inserted 
in  the  mouth. 

A  skilful  telegraphist  can  transmit  twenty-five 
words  a  minute  with  the  single-current  key,  and 
nearly  twice  as  many  by  the  double-current  key, 
and  if  we  remember  that  an  average  English 
word  requires  fifteen  separate  signals,  the  num- 
ber will  seem  remarkable ;  but  by  means  of 
Wheatstone's  automatic  sender  150  words  or 
more  can  be  sent  in  a  minute. 

Among  telegraphs  designed  to  print  the  mes- 
sage in  Roman  type,  that  of  Professor  David 
Edward  Hughes  is  doubtless  the  fittest,  since  it 
is  now  in  general  use  on  the  Continent,  and  con- 
veys our  Continental  news.  In  this  apparatus 
the  electromagnet,  on  attracting  its  armature, 
presses  the  paper  against  a  revolving  type  wheel 
and  receives  the  print  of  a  type,  so  that  the  mes- 


92  THE  STORY  OF   ELECTRICITY. 

sage  can  be  read  by  a  novice.  To  this  effect  the 
type  wheel  at  the  receiving  station  has  to  keep  in 
perfect  time  as  it  revolves,  so  that  the  right  letter 
shall  be  above  the  paper  when  the  current  passes. 
Small  varieties  of  the  type-printer  are  employed 
for  the  distribution  of  news  and  prices  in  most  of 
the  large  towns,  being  located  in  hotels,  restau- 
rants, saloons,  and  other  public  places,  and  re- 
porting prices  of  stocks  and  bonds,  horse  races, 
and  sporting  and  general  news.  The  "  duplex 
system,"  whereby  two  messages,  one  in  either 
direction,  can  be  sent  over  one  wire  simultane- 
ously without  interfering,  and  the  quadruplex 
system,  whereby  four  messages,  two  in  either 
direction,  are  also  sent  at  once,  have  come  into 
use  where  the  traffic  over  the  lines  is  very  great. 
Both  of  these  systems  and  their  modifications 
depend  on  an  ingenious  arrangement  of  the  ap- 
paratus at  each  end  of  the  line,  by  which  the 
signal  currents  sent  out  from  one  station  do  not 
influence  the  receivers  there,  but  leave  them  free 
to  indicate  the  currents  from  the  distant  station. 
When  the  Wheatstone  Automatic  Sender  is  em- 
ployed with  these  systems  about  500  words  per 
minute  can  be  sent  through  the  line.  Press  news 
is  generally  sent  by  night,  and  it  is  on  record, 
that  during  a  great  debate  in  Parliament,  as  many 
as  half  a  million  words  poured  out  of  the  Central 
Telegraph  Station  at  St.  Martin's-le-Grand  in  a 
single  night  to  all  parts  of  the  country. 

Errors  occur  now  and  then  through  bad  pen- 
manship or  the  similarity  of  certain  signals,  and 
amusing  telegrams  have  been  sent  out,  as  when 
the  nomination  of  Mr.  Brand  for  the  Speakership 
of  the  Commons  took  the  form  of  "Proposed  to 
brand  Speaker  "  ;  and  an  excursion  party  assured 


THE  TELEGRAPH  AND  TELEPHONE.     93 

their  friends  at  home  of  their  security  by  the 
message,  "  Arrived  all  tight." 

Telegraphs,  in  the  literal  sense  of  the  word, 
which  actually  write  the  message  as  with  a  pen, 
and  make  a  copy  or  facsimile  of  the  original, 
have  been  invented  from  time  to  time.  Such  are 
the  "telegraphic  pen  "  of  Mr.  E.  A.  Cowper,  and 
the  "telautographs"  of  Mr.  J.  H.  Robertson  and 
Mr.  Elisha  Gray.  The  first  two  are  based  on  a 
method  of  varying  the  strength  of  the  current 
in  accordance  with  the  curves  of  the  handwriting, 
and  making  the  varied  current  actuate  by  means 
of  magnetism  a  writing  pen  or  stylus  at  the 
distant  station.  The  instrument  of  Gray,  which 
is  the  most  successful,  works  by  intermittent 
currents  or  electrical  impulses,  that  excite 
electro-magnets  and  move  the  stylus  at  the  far 
end  of  the  line.  They  are  too  complicated  for 
description  here,  and  are  not  of  much  practical 
importance. 

Telegraphs  for  transmitting  sketches  and  draw- 
ings have  also  been  devised  by  D'Ablincourt  and 
others,  but  they  have  not  come  into  general  use. 
Of  late  another  step  forward  has  been  taken  by 
Mr.  Amstutz,  who  has  invented  an  apparatus  for 
transmitting  photographic  pictures  to  a  distance 
by  means  of  electricity.  The  system  may  be 
described  as  a  combination  of  the  photograph 
and  telegraph.  An  ordinary  negative  picture  is 
taken,  and  then  impressed  on  a  gelatine  plate 
sensitised  with  bichromate  of  potash.  The  parts 
of  the  gelatine  in  light  become  insoluble,  while 
the  parts  in  shade  can  be  washed  away  by  water. 
In  this  way  a  relief  or  engraving  of  the  picture 
is  obtained  on  the  gelatine,  and  a  cross  section 
through  the  plate  would,  if  looked  at  edgeways, 


94  THE  STORY   OF   ELECTRICITY. 

appear  serrated,  or  up  and  down,  like  a  section 
of  country  or  the  trace  of  the  stylus  in  the  record 
of  a  phonograph.  The  gelatine  plate  thus  carved 
by  the  action  of  light  and  water  is  wrapped  round 
a  revolving  drum  or  barrel,  and  a  spring  stylus  or 
point  is  caused  to  pass  over  it  as  the  barrel  re- 
volves, after  the  manner  of  a  phonographic  cylin- 
der. In  doing  so  the  stylus  rises  and  falls  over 
the  projections  in  the  plate  and  works  a  lever 
against  a  set  of  telegraph  keys,  which  open  elec- 
tric contacts  and  break  the  connections  of  an 
electric  battery  which  is  joined  between  the  keys 
and  the  earth.  There  are  four  keys,  and  when 
they  are  untouched  the  current  splits  up  through 
four  by-paths  or  bobbins  of  wire  before  it  enters 
the  line  wire  and  passes  to  the  distant  station. 
When  any  of  the  keys  are  touched,  however,  the 
corresponding  by-path  or  bobbin  is  cut  out  of 
circuit.  The  suppression  of  a  by-path  or  channel 
for  the  current  has  the  effect  of  adding  to  the  "  re- 
sistance "  of  the  line,  and  therefore  of  diminishing 
the  strength  of  the  current.  When  all  the  keys 
are  untouched  the  resistance  is  least  and  the  cur- 
rent strongest.  On  the  other  hand,  when  all  the 
keys  but  the  last  are  touched,  the  resistance  is 
greatest  and  the  current  weakest.  By  this  device 
it  is  easy  to  see  that  as  the  stylus  or  tracer  sinks 
into  a  hollow  of  the  gelatine,  or  rises  over  a 
height,  the  current  in  the  line  becomes  stronger 
or  weaker.  At  the  distant  station  the  current 
passes  through  a  solenoid  or  hollow  coil  of  wire 
connected  to  the  earth  and  magnetises  it,  so  as 
to  pull  the  soft  iron  plug  or  "  core  "  with  greater 
or  less  force  into  its  hollow  interior.  The  up  and 
down  movement  of  the  ping  actuates  a  graving 
stylus  or  point  through  a  lever,  and  engraves  a 


THE  TELEGRAPH  AND  TELEPHONE.     95 

copy  of  the  original  gelatine  trace  on  the  surface 
of  a  wax  or  gelatine  plate  overlying  another 
barrel  or  drum,  which  revolves  at  a  rate  corre- 
sponding to  that  of  the  barrel  at  the  transmitting 
station.  In  this  way  a  facsimile  of  the  gelatine 
picture  is  produced  at  the  distant  station,  and  an 
electrotype  or  cliche  of  it  can  be  made  for  printing 
purposes.  The  method  is,  in  fact,  a  species  of 
electric  line  graving,  and  Mr.  Amstutz  hopes  to 
apply  it  to  engraving  on  gold,  silver,  or  any  soft 
metal,  not  necessarily  at  a  distance. 

We  know  that  an  electric  current  in  one  wire 
can  induce  a  transient  current  in  a  neighbouring 
wire,  and  the  fact  has  been  utilised  in  the  United 
States  by  Phelps  and  others  to  send  messages 
from  moving  trains.  The  signal  currents  are 
intermittent,  and  when  they  are  passed  through  a 
conductor  on  the  train  they  excite  corresponding 
currents  in  a  wire  run  along  the  track,  which  can 
be  interpreted  by  the  hum  they  make  in  a  tele- 
phone. Experiments  recently  made  by  Mr.  W.  H. 
Preece  for  the  Post  Office  show  that  with  currents 
of  sufficient  strength  and  proper  apparatus  mes- 
sages can  be  sent  through  the  air  for  five  miles 
or  more  by  this  method  of  induction. 

We  come  now  to  the  submarine  telegraph, 
which  differs  in  many  respects  from  the  overland 
telegraph.  Obviously,  since  water  and  moist 
earth  is  a  conductor,  a  wire  to  convey  an  electric 
current  must  be  insulated  if  it  is  intended  to  lie 
at  the  bottom  of  the  sea  or  buried  underground. 
The  best  materials  for  the  purpose  yet  discovered 
are  gutta-percha  and  india-rubber,  which  are  both 
flexible  and  very  good  insulators. 

The  first  submarine  cable  was  laid  across  the 
Channel  from  Dover  to  Calais  in  1851,  and  con- 


96 


THE   STORY  OF   ELECTRICITY. 


sisted  of  a  copper  strand,  coated  with  gutta- 
percha,  and  protected  from  injury  by  an  outer 
sheath  of  hemp  and  iron  wire.  It  is  the  general 
type  of  all  the  submarine  cables  which  have  been 
deposited  since  then  in  every  part  of  the  world. 
As  a  rule,  the  armour  or  sheathing  is  made 
heavier  for  shore  water  than  it  is  for  the  deep 
sea,  but  the  electrical  portion,  or  "  core,"  that 


Irish  Shore  End. 
FIG.  51.— SECTION  OF  THE  1894  ATLANTIC  CABLE— ACTUAL  SIZE. 

is  to  say,  the  insulated   conductor,   is  the  same 
throughout. 

The  first  Atlantic  cable  was  laid  in  1858  by 
Cyrus  W.  Field  and  a  company  of  British  capital- 
ists, but  it  broke  down,  and  it  was  not  until  1866 
that  a  new  and  successful  cable  was  laid  to  re- 


THE  TELEGRAPH  AND  TELEPHONE. 


97 


place    it.      Figure    51    represents    various    cross- 
sections  of  an  Atlantic  cable  deposited  in  1894. 


Light  Intermediate. 

Heavy  Intermediate. 

SECTIONS  OF  THE  1894  ATLANTIC  CABLE—ACTUAL  SIZES— 
continued. 

The  inner  star  of  twelve  copper  wires  is  the  con- 
ductor, and  the  black  circle  round  it  is  the  gutta- 
7 


98  THE  STORY  OF  ELECTRICITY. 

percha  or  insulator  which  keeps  the  electricity 
from  escaping  into  the  water.  The  core  in  shallow 
water  is  protected  from  the  bites  of  teredoes  by  a 
brass  tape,  and  the  envelope  or  armour  consists  of 
hemp  and  iron  wire  preserved  from  corrosion  by 
a  covering  of  tape  and  a  compound  of  mineral 
pitch  and  sand. 

The  circuit  of  a  submarine  line  is  essentially 
the  same  as  that  of  a  land  line,  except  that  the 
earth  connection  is  usually  the  iron  sheathing  of 
the  cable  in  lieu  of  an  earth-plate.  On  a  cable, 
however,  at  least  a  long  cable,  the  instruments  for 
sending  and  receiving  the  messages  are  different 
from  those  employed  on  a  land  line.  A  cable  is 
virtually  a  Leyden  jar  or  condenser,  and  the  signal 
currents  in  the  wire  induce  opposite  currents  in 
the  water  or  earth.  As  these  charges  hold  each 


FIG.  52. 

other  the  signals  are  retarded  in  their  progress, 
and  altered  from  sharp  sudden  jets  to  lagging  un- 
dulations or  waves,  which  tend  to  run  together  or 
coalesce.  The  result  is  that  the  separate  signal 
currents  which  enter  a  long  cable  issue  from  it  at 
the  other  end  in  one  continuous  current,  with  pul- 
sations at  every  signal,  that  is  to  say,  in  a  lapsing 
stream,  like  a  jet  of  water  flowing  from  a  con- 
stricted spout.  The  receiving  instrument  must 


THE  TELEGRAPH  AND  TELEPHONE.     99 

be  sufficiently  delicate  to  manifest  every  pulsation 
of  the  current.  Its  indicator,  in  fact,  must  re- 
spond to  every  rise  and  fall  of  the  current,  as  a 
float  rides  on  the  ripples  of  a  stream. 

Such  an  instrument  is  the  beautiful  "mirror" 
galvanometer  of  Lord  Kelvin,  Ex-President  of  the 
Royal  Society,  which  we  illustrate  in  figure  52, 
where  C  is  a  coil  of  wire  with  a  small  magnetic 
needle  suspended  in  its  heart,  and  D  is  a  steel 
magnet  supported  over  it.  The  needle  (M  figure 
53)  is  made  of  watch  spring  cemented  to  the  back 
of  a  tiny  mirror  the  size  of  a  half-dime 
which  is  hung  by  a  single  fibre  of  floss 
silk  inside  an  air  cell  or  chamber  with  a 
glass  lens  G  in  front,  and  the  coil  C  sur- 
rounds it.  A  ray  of  light  from  a  lamp 
L  (figure  52)  falls  on  the  mirror,  and  is 
reflected  back  to  a  scale  S,  on  which  it 
makes  a  bright  spot.  Now,  when  the 
coil  C  is  connected  between  the  end  of 
the  cable  and  the  earth,  the  signal  current  passing 
through  it  causes  the  tiny  magnet  to  swing  from 
side  to  side,  and  the  mirror  moving  with  it  throws 
the  beam  up  and  down  the  scale.  The  operator 
sitting  by  watches  the  spot  of  light  as  it  flits  and 
flickers  like  a  fire-fly  in  the  darkness,  and  spells 
out  the  mysterious  message. 

A  condenser  joined  in  the  circuit  between  the 
cable  and  the  receiver,  or  between  the  receiver 
and  the  earth,  has  the  effect  of  sharpening  the 
waves  of  the  current,  and  consequently  of  the 
signals.  The  double-current  key,  which  reverses 
the  poles  of  the  battery  and  allows  the  signal 
currents  to  be  of  one  length,  that  is  to  say,  all 
"dots,"  is  employed  to  send  the  message. 

Another   receiving    instrument    employed   on 


100 


THE  STORY  OF   ELECTRICITY. 


most  of  the  longer  cables  is  the 
siphon  recorder  of  Lord  Kelvin, 
shown  in  figure  54,  which  marks 
or  writes  the  message  on  a  slip 
of  travelling  paper.     Essentially 
it  is  the  inverse  of  the  mir- 
ror   instrument,    and    con- 
sists of  a  light  coil  of  wire 
61  suspended 
in  the   field 
between  the 
poles    of    a 
strong  mag- 
net M.    The 
coil    is    at- 
tached      to 
a  fine   siphon  (P) 


filled  with  ink,  and 
sometimes  kept  in 
vibration  by  an  in- 
duction coil  so  as 
to  shake  the  ink 
in  fine  drops  upon 
a  slip  of  mov- 
ing paper.  The 
coil  is  connected 
between  the  cable 
and  the  earth,  and, 
as  the  signal 
current  passes 
through,  it  swings 
to  one  side  or  the 
other,  pulling  the 
siphon  with  it.  FIG.  54. 

The  ink,  therefore, 
marks  a  wavy  line  on  the  paper,  which  is  in  fact  a 


THE  TELEGRAPH  AND  TELEPHONE.     IOI 

delineation  of  the  rise  and  fall  of  the  signal  current 
and  a  record  of  the  message.  The  dots  in  this 
case  are  represented  by  the  waves  above,  and  the 
"  dashes  "  by  the  waves  below  the  middle  line,  as 
may  be  seen  in  the  following  alphabet,  which  is  a 


FIG.  55- 

copy  of  one  actually  written  by  the  recorder  on  a 
long  submarine  cable. 

Owing  to  induction,  the  speed  of  signalling  on 
long  cables  is  much  slower  than  on  land  lines  of 
the  same  length,  and  only  reaches  from  25  to  45 
words  a  minute  on  the  Atlantic  cables,  or  30  to 
50  words  with  an  automatic  sending-key  ;  but  this 
rate  is  practically  doubled  by  employing  the  Muir- 
head  duplex  system  of  sending  two  messages,  one 
from  each  end,  at  the  same  time. 

The  relation  of  the  telegraph  to  the  telephone 
is  analogous  to  that  of  the  lower  animals  and 
man.  In  a  telegraph  circuit,  with  its  clicking  key 
at  one  end  and  its  chattering  sounder  at  the  other, 
we  have,  in  fact,  an  apish  forerunner  of  the  ex- 
quisite telephone,  with  its  mysterious  microphone 
and  oracular  plate.  Nevertheless,  the  telephone 
descended  from  the  telegraph  in  a  very  indirect 
manner,  if  at  all,  and  certainly  not  through  the 


THE   STORY  OF   ELECTRICITY. 


sounder.  The  first  practical  suggestion  of  an 
electric  telephone  was  made  by  M.  Charles  Bour- 
seul,  a  French  telegraphist,  in  1854,  but  to  all  ap- 
pearance nothing  came  of  it.  In  1860,  however, 
Philipp  Reis,  a  German  schoolmaster,  constructed 
a  rudimentary  telephone,  by  which  music  and  a 
few  spoken  words  were  sent.  Finally,  in  1876, 
Mr.  Alexander  Graham  Bell,  a  Scotchman,  residing 
in  Canada,  and  subsequently  in  the  United  States, 
exhibited  a  capable  speaking  telephone  of  his  in- 
vention at  the  Centennial  Exhibition,  Philadel- 
phia. 

Figure  56  represents  an  outside  view  and  sec- 
tion of  the  Bell  telephone  as  it  is  now  made,  where 
M  is  a  bar  magnet  having 
a  small  bobbin  or  coil  of 
fine  insulated  wire  C  gir- 
dling one  pole.  In  front 
of  this  coil  there  is  a  cir- 
cular plate  of  soft  iron 
capable  of  vibrating  like  a 
diaphragm  or  the  drum  of 
the  ear.  A  cover  shaped 
like  a  mouthpiece  O  fixes 
the  diaphragm  all  round, 
and  the  wires  W  W  serve 
to  connect  the  coil  in  the 
circuit. 

The  soft  iron  diaphragm 
is,    of    course,    magnetised 
FIG.  56.  by    the    induction    of    the 

pole,    and    would    be     at- 

tracte'd  bodily  to  the  pole  were  it  not  fixed  by 
the  rim,  so  that  only  its  middle  is  free  to  move. 
Now,  when  a  person  speaks  into  the  mouthpiece 
the  sonorous  waves  impinge  on  the  diaphragm 


THE  TELEGRAPH  AND  TELEPHONE.    103 

and  make  it  vibrate  in  sympathy  with  them.  Be- 
ing magnetic,  the  movement  of  the  diaphragm 
to  and  from  the  bobbin  excites  corresponding 
waves  of  electricity  in  the  coil,  after  the  famous 
experiment  of  Faraday  (page  64).  If  this  undula- 
tory  current  is  passed  through  the  coil  of  a  similar 
telephone  at  the  far  end  of  the  line,  it  will,  by  a 
reverse  action,  set  the  diaphragm  in  vibration  and 
reproduce  the  original  sonorous  waves.  The  re- 
sult is,  that  when  another  person  listens  at  the 
mouthpiece  of  the  receiving  telephone,  he  will 
hear  a  faithful  imitation  of  the  original  speech. 

The  Bell  telephone  is  virtually  a  small  mag- 
neto-electric generator  of  electricity,  and  when 
two  are  joined  in  circuit  we  have  a  system  for  the 
transmission  of  energy.  As  the  voice  is  the  mo- 
tive power,  its  talk,  though  distinct,  is  compara- 
tively feeble,  and  further  improvements  were 
made  before  the  telephone  became  as  serviceable 
as  it  is  now. 

Edison,  in  1877,  was  the  first  to  invent  a  work- 
ing telephone,  which,  instead  of  generating  the 
current,  merely  controlled  the  strength  of  it,  as 
the  sluice  of  a  mill-dam  regulates  the  flow  of  water 
in  the  lead.  Du  Moncel  had  observed  that  powder 
of  carbon  altered  in  electrical  resistance  under 
pressure,  and  Edison  found  that  lamp-black  was  so 
sensitive  as  to  change  in  resistance  under  the  im- 
pact of  the  sonorous  waves.  His  transmitter  con- 
sisted of  a  button  or  wafer  of  lamp-black  behind 
a  diaphragm,  and  connected  in  the  circuit.  On 
speaking  to  the  diaphragm  the  sonorous  waves 
pressed  it  against  the  button,  and  so  varied  the 
strength  of  the  current  in  a  sympathetic  manner. 
The  receiver  of  Edison  was  equally  ingenious, 
and  consisted  of  a  cylinder  of  orepared  chalk  kept 


104  THE  STORY  OF  ELECTRICITY. 

in  rotation  and  a  brass  stylus  rubbing  on  it. 
When  the  undulatory  current  passed  from  the 
stylus  to  the  chalk,  the  stylus  slipped  on  the  sur- 
face, and,  being  connected  to  a  diaphragm,  made 
it  vibrate  and  repeat  the  original  sounds.  This 
"  electro-motograph  "  receiver  was,  however, 
given  up,  and  a  combination  of  the  Edison  trans- 
mitter and  the  Bell  receiver  came  into  use. 

At  the  end  of  1877  Professor  D.  E.  Hughes,  a 
distinguished  Welshman,  inventor  of  the  printing 
telegraph,  discovered  that  any  loose  contact  be- 
tween two  conductors  had  the  property  of  trans- 
mitting sounds  by  varying  the  strength  of  an 
electric  current  passing  through  it.  Two  pieces 
of  metal — for  instance,  two  nails  or  ends  of  wire 
— when  brought  into  a  loose  or  crazy  contact 
under  a  slight  pressure,  and  traversed  by  a  cur- 
rent, will  transmit  speech.  Two  pieces  of  hard 
carbon  are  still  better  than  metals,  and  if  prop- 
erly adjusted  will  make  the  tread  of  a  fly  quite 
audible  in  a  telephone  connected  with  them. 
Such  is  the  famous  "  mi- 
crophone," by  which  a 
faint  sound  can  be 
magnified  to  the 
ear. 

Figure  57  represents 
what  is  known  as  the  "  pen- 
cil "  microphone,  in  which  M 
is  a  pointed  rod  of  hard  car- 
bon,   delicately    poised     be- 
tween two  brackets  of  carbon,  FIG.  57. 
which  are   connected   in   cir- 
cuit with  a  battery  B  and  a  Bell  telephone  T.    The 
joints  of  rod  and  bracket  are  so  sensitive  that  the 
current  flowing  across  them  is  affected  in  strength 


M 


THE  TELEGRAPH  AND  TELEPHONE.     105 

by  the  slightest  vibration,  even  the  walking  of  an 
insect.  If,  therefore,  we  speak  near  this  micro- 
phone, the  sonorous  waves,  causing  the  pencil  to 
vibrate,  will  so  vary  the  current  in  accordance 
with  them  as  to  reproduce  the  sounds  of  the  voice 
in  the  telephone. 

The  true  nature  of  the  microphone  is  not  yet 
known,  but  it  is  evident  that  the  air  or  ether  be- 
tween the  surfaces  in  contact  plays  an  important 
part  in  varying  the  resistance,  and,  therefore, 
the  current.  In  fact,  a  small  "  voltaic  arc,"  not 
luminous,  but  dark,  seems  to  be  formed  between 
the  points,  and  the  vibrations  probably  alter  its 
length,  and,  consequently,  its  resistance.  The 
fact  that  a  microphone  is  reversible  and  can  act 
as  a  receiver,  though  a  poor  one,  tends  to  confirm 
this  theory.  Moreover,  it  is  not  unlikely  that  the 
slipping  of  the  stylus  in  the  electromotograph  is 
due  to  a  similar  cause.  Be  this  as  it  may,  there 
can  be  no  doubt  that  carbon  powder  and  the 
lamp-black  of  the  Edison  button  are  essentially  a 
cluster  of  microphones. 

Many  varieties  of  the  Hughes  microphone  un- 
der different  names  are  now  employed  as  transmit- 
ters in  connection  with  the  Bell  telephone.  Figure 
58  represents  a  simple  micro-telephone  circuit, 
where  M  is  the  Hughes  microphone  transmitter, 
T  the  Bell  telephone  receiver,  B  the  battery,  and 
E  E  the  earth-plates ;  but  sometimes  a  return 
wire  is  used  in  place  of  the  "  earth." 

The  line  wire  is  usually  of  copper  and  its 
alloys,  which  are  more  suitable  than  iron,  especi- 
ally for  long  distances.  Just  as  the  signal  cur- 
rents in  a  submarine  cable  induce  corresponding 
currents  in  the  sea  water  which  retard  them,  so 
the  currents  in  a  land  wire  incjuce  corresponding 


io6 


THE   STORY   OF   ELECTRICITY. 


currents  in  the  earth,  but  in  aerial  lines  the  earth 
is  generally  so  far  away  that  the  consequent  re- 
tardation is  negligible  except  in  fast  working  on 
long  lines.  The  Bell  telephone,  however,  is  ex- 
tremely sensitive,  and  this  induction  affects  it  so 


FIG.  58. 

much  that  a  conversation  through  one  wire  can 
be  overheard  on  a  neighbouring  wire.  Moreover, 
there  is  such  a  thing  as  u  self-induction  "  in  a  wire 
— that  is  to  say,  a  current  in  a  wire  tends  to  in- 
duce an  opposite  current  in  the  same  wire,  which 
is  practically  equivalent  to  an  increase  of  resist- 
ance in  the  wire.  It  is  particularly  observed  at 
the  starting  and  stopping  of  a  current,  and  gives 
rise  to  what  is  called  the  "extra-spark"  seen  in 
breaking  the  circuit  of  an  induction  coil.  It  is 
also  active  in  the  vibratory  currents  of  the  tele- 
phone, and,  like  ordinary  induction,  tends  to 
retard  their  passage.  Copper  being  less  suscep- 
tible of  self-induction  than  iron,  is  preferred  for 
trunk  lines.  The  disturbing  effect  of  ordinary 
induction  is  avoided  by  using  a  return  wire  or 
loop  circuit,  and  crossing  the  going  and  coming 
wires  so  as  to  make  them  exchange  places  at 
intervals.  Moreover,  it  is  found  that  an  indue- 


THE  TELEGRAPH  AND  TELEPHONE.    107 

tion  coil  in  the  telephone  circuit,  like  a  condenser 
in  the  cable  circuit,  improves  the  working,  and 
hence  it  is  usual  to  join  the  battery  and  trans- 
mitter with  the  primary  wire,  and  the  secondary 
wire  with  the  line  and  the  receiver. 

The  longest  telephone  line  as  yet  made  is  that 
from  New  York  to  Chicago,  a  distance  of  950 
miles.  It  is  made  of  thick  copper  wire,  erected 
on  cedar  poles  35  feet  above  the  ground. 

Induction  is  so  strong  on  submarine  cables  of 
50  or  100  miles  in  length  that  the  delicate  waves 
of  the  telephone  current  are  smoothed  away,  and 
the  speech  is  either  muffled  or  entirely  stifled. 
Nevertheless,  a  telephone  cable  20  miles  long 
was  laid  between  Dover  and  Calais  in  1891,  and 
another  between  Stranraer  and  Donaghadee  more 
recently,  thus  placing  Great  Britain  on  speaking 
terms  with  France  and  other  parts  of  the  Con- 
tinent. 

Figure  59  shows  a  form  of  telephone  appara- 
tus employed  in  the  United  Kingdom.  In  it  the 
transmitter  and  receiver,  together  with  a  call-bell, 
which  are  required  at  each  end  of  the  line,  are 
neatly  combined.  The  transmitter  is  a  Blake 
microphone,  in  which  the  loose  joint  is  a  contact 
of  platinum  on  hard  carbon.  It  is  fitted  up  in- 
side the  box,  together  with  an  induction  coil, 
and  M  is  the  mouthpiece  for  speaking  to  it.  The 
receiver  is.  a  pair  of  Bell  telephones  T  T,  which 
are  detached  from  their  hooks  and  held  to  the 
ear.  A  call-bell  B  serves  to  "  ring  up  "  the  cor- 
respondent at  the  other  end  of  the  line. 

Excepting  private  lines,  the  telephone  is 
worked  on  the  "  exchange  system  " — that  is  to 
say,  the  wires  running  to  different  persons  con- 
verge in  a  central  exchange,  where,  by  means  of 


io8 


THE   STORY   OF   ELECTRICITY. 


an  apparatus  called  a  "  switch-board,"  they  are 
connected  together  for  the  purpose  of  conversa- 
tion. 

A  telephone  exchange  would  make  an  excel- 


Fro.  59. 


lent  subject  for  the  artist.  He  delights  to  paint 
us  a  row  of  Venetian  bead-stringers  or  a  band  of 
Sevillian  cigarette-makers,  but  why  does  he  shirk 
a  bevy  of  industrious  girls  working  a  telephone 
exchange  ?  Let  us  peep  into  one  of  these  retired 
haunts,  where  the  modern  Fates  are  cutting  and 


THE  TELEGRAPH  AND  TELEPHONE.    109 

joining  the  lines  of  electric  speech  between  man 
and  man  in  a  great  city. 

The  scene  is  a  long,  handsome  room  or  gal- 
lery, with  a  singular  piece  of  furniture  in  the 
shape  of  an  L  occupying  the  middle.  This  is  the 
switchboard,  in  which  the  wires  from  the  offices 
and  homes  of  the  subscribers  are  concentrated 
like  the  nerves  in  a  ganglion.  It  is  known  as  the 
u  multiple  switchboard,"  an  American  invention, 
and  is  divided  into  sections,  over  which  the  oper- 
ators preside.  The  lines  of  all  the  subscribers 
are  brought  to  each  section,  so  that  the  operator 
can  cross-connect  any  two  lines  in  the  whole  sys- 
tem without  leaving  her  chair.  Each  section  of 
the  board  is,  in  fact,  an  epitome  of  the  whole,  but 
it  is  physically  impossible  for  a  single  operator  to 
make  all  the  connections  of  a  large  exchange,  and 
the  work  is  distributed  amongst  them.  A  multi- 
plicity of  wires  is  therefore  needed  to  connect, 
say,  two  thousand  subscribers.  These  are  all 
concealed,  however,  at  the  back  of  the  board, 
and  in  charge  of  the  electricians.  The  young 
lady  operators  have  nothing  to  do  with  these, 
and  so  much  the  better  for  them,  as  it  would 
puzzle  their  minds  a  good  deal  worse  than  a  rav- 
elled skein  of  thread.  Their  duty  is  to  sit  in 
front  of  the  board  in  comfortable  seats  at  a  long 
table  and  make  the  needful  connections.  The 
call-signal  of  a  subscriber  is  given  by  the  drop  of 
a  disc  bearing  his  number.  The  operator  then 
asks  the  subscriber  by  telephone  what  he  wants, 
and  on  hearing  the  number  of  the  other  sub- 
scriber he  wishes  to  speak  with,  she  takes  up  a 
pair  of  brass  plugs  coupled  by  a  flexible  con- 
ductor and  joins  the  lines  of  the  subscribers  on 
the  switchboard  by  simply  thrusting  the  plugs 


110  THE  STORY   OF  ELECTRICITY. 

into  holes  corresponding  to  the  wires.  The  sub- 
scribers are  then  free  to  talk  with  each  other 
undisturbed,  and  the  end  of  the  conversation  is 
signalled  to  the  operator.  Every  instant  the  call 
discs  are  dropping,  the  connecting  plugs  are 
thrust  into  the  holes,  and  the  girls  are  asking, 
"  Hullo  !  hullo!"  "  Are  you  there  ?"  "Who  are 
you  ? "  "  Have  you  finished  ?  "  Yet  all  this  con- 
stant activity  goes  on  quietly,  deftly — we  might 
say  elegantly — and  in  comparative  silence,  for  the 
low  tones  of  the  girlish  voices  are  soft  and  pleas- 
ing, and  the  harsher  sounds  of  the  subscriber  are 
unheard  in  the  room  by  all  save  the  operator  who 
attends  to  him. 


CHAPTER  VII. 

ELECTRIC    LIGHT    AND    HEAT. 

THE  electric  spark  was,  of  course,  familiar  to 
the  early  experimenters  with  electricity,  but  the 
electric  light,  as  we  know  it,  was  first  discovered 
by  Sir  Humphrey  Davy,  the  Cornish  philosopher, 
in  the  year  1811  or  thereabout.  With  the  magic 
of  his  genius  Davy  transformed  the  spark  into  a 
brilliant  glow  by  passing  it  between  two  points  of 
carbon  instead  of  metal.  If,  as  in  figure  60,  we 
twist  the  wires  (+  and  — )  which  come  from  a 
voltaic  battery,  say  of  20  cells,  about  two  carbon 
pencils,  and  bring  their  tips  together  in  order  to 
start  the  current,  then  draw  them  a  little  apart, 
we  shall  produce  an  artificial  or  mimic  star.  A 
sheet  of  dazzling  light,  which  is  called  the  elec- 
tric arc,  is  seen  to  bridge  the  gap.  It  is  not  a 


ELECTRIC   LIGHT  AND   HEAT.  m 

true  flame,  for  there  is  little  combustion,  but 
rather  a  nebulous  blaze  of  silvery  lustre  in  a 
bluish  veil  of  heated  air. 
The  points  of  carbon  are 
white-hot,  and  the  positive 
is  eaten  away  into  a  hol- 
low or  crater  by  the  cur- 
rent, which  violently  tears 
its  particles  from  their  seat 
and  whirls  them  into  the 
fierce  vortex  of  the  arc. 
The  negative  remains 
pointed,  but  it  is  also  worn 
away  about  half  as  fast  as  FIG.  60. 

the  positive.  This  wasting 
of  the  carbons  tends  to  widen  the  arc  too  much 
and  break  the  current,  hence  in  arc  lamps  meant 
to  yield  the  light  for  hours  the  sticks  are  made  of 
a  good  length,  and  a  self-acting  mechanism  feeds 
them  forward  to  the  arc  as  they  are  slowly  con- 
sumed, thus  maintaining  the  splendour  of  the 
illumination. 

Many  ingenious  lamps  have  been  devised  by 
Serrin,  Dubosq,  Siemens,  Brockie,  and  others, 
some  regulating  the  arc  by  clockwork  and  elec- 
tro-magnetism, or  by  thermal  and  other  effects  of 
the  current.  They  are  chiefly  used  for  lighting 
halls  and  railway  stations,  streets  and  open  spaces, 
search-lights  and  lighthouses.  They  are  some- 
times naked,  but  as  a  rule  their  brightness  is  tem- 
pered by  globes  of  ground  or  opal  glass.  In 
search-lights  a  parabolic  mirror  projects  all  the 
rays  in  any  one  direction,  and  in  lighthouses  the 
arc  is  placed  in  the  focus  of  the  condensing  lenses, 
and  the  beam  is  visible  for  at  least  twenty  or 
thirty  miles  on  clear  nights.  Very  powerful  arc 


112 


THE  STORY   OF   ELECTRICITY. 


lights,  equivalent   to   hundreds   of  thousands  of 
candles,  can  be  seen  for  100  or  150  miles. 

Figure  61  illustrates  the  Pilsen  lamp,  in  which 
the  positive  carbon  G  runs  on  rollers  r  r  through 
the  hollow  interior  of  two  solenoids  or  coils  of 


FIG.  61.— The  Pilsen  Lamp. 


wire  MM1  and  carries  at  its  middle  a  spindle- 
shaped  piece  of  soft  iron  C.  The  current  flows 
through  the  solenoid  M  on  its  way  to  the  arc,  but 
a  branch  or  shunted  portion  of  it  flows  through 
the  solenoid  M\  and  as  both  of  these  solenoids 
act  as  electromagnets  on  the  soft  iron  (7,  each 
tending  to  suck  it  into  its  interior,  the  iron  rests 
between  them  when  their  powers  are  balanced. 
When,  however,  the  arc  grows  too  wide,  and  the 
current  therefore  becomes  too  weak,  the  shunt 
solenoid  M1  gains  a  purchase  over  the  main  sole- 
noid M,  and,  pulling  the  iron  core  towards  it, 
feeds  the  positive  carbon  to  the  arc.  In  this  way 
the  balance  of  the  solenoids  is  readjusted,  the 
current  regains  its  normal  strength,  the  arc  its 
proper  width,  and  the  light  its  brilliancy. 

Figure  62  is  a  diagrammatic  representation  of 
the  Brush  arc  lamp.  X  and  Y  are  the  line  ter- 
minals connecting  the  lamp  in  circuit.  On  the 


ELECTRIC   LIGHT  AND   HEAT.  113 

one  hand,  the  current  splits  and  passes  around 
the  hollow  spools  H  H',  thence  to  the  rod  N 


FIG.  62. — The  Brush  Lamp. 


through  the  carbon  K,  the  arc,  the  carbon  K',  and 
thence  through  the  lamp  frame  to  Y.  On  the 
other  hand,  it  runs  in  a  resistance  fine-wire  coil 
around  the  magnet  T,  thence  to  Y.  The  opera- 
tion of  the  lamp  is  as  follows :  K  and  Kl  being 
in  contact,  a  strong  current  starts  through  the 
lamp  energising  H  and  H',  which  suck  in  their 
core  pieces  N  and  S,  lifting  (7,  and  by  it  the 
"  washer-clutch  "  W^and  the  rod  Nand  carbon  K, 
establishing  the  arc.  Kis  lifted  until  the  increas- 
ing resistance  of  the  lengthening  arc  weakens  the 
current  in  H  H'  and  a  balance  is  established.  As 
the  carbons  burn  away,  C  gradually  lowers  until 
a  stop  under  W  holds  it  horizontal  and  allows  N 
to  drop  through  W,  and  the  lamp  starts  anew.  If 
for  any  reason  the  resistance  of  the  lamp  becomes 
8 


114  THE   STORY  OF  ELECTRICITY. 

too  great,  or  the  circuit  is  broken,  the  increased 
current  through  T  draws  up  its  armature,  closing 
the  contacts  J/,  thus  short-circuiting  the  lamp 
through  a  thick,  heavy  wire  coil  on  7",  which  then 
keeps  M  closed,  and  prevents  the  dead  lamp  from 
interfering  with  the  others  on  its  line.  Numer- 
ous modifications  of  this  lamp  are  in  very  gen- 
eral use. 

Davy  also  found  that  a  continuous  wire  or 
stick  of  carbon  could  be  made  white-hot  by  send- 
ing a  sufficient  current  through  it,  and  this  fact  is 
the  basis  of  the  incandescent  lamp  now  so  common 
in  our  homes. 

Wires  of  platinum,  iridium,  and  other  inoxi- 
disable  metals  raised  to  incandescence  by  the 
current  are  useful  in  firing  mines,  but  they  are 
not  quite  suitable  for  yielding  a  light,  because  at 
a  very  high  temperature  they  begin  to  melt. 
Every  solid  body  becomes  red-hot — that  is  to  say, 
emits  rays  of  red  light,  at  a  temperature  of  about 
1000°  Fahrenheit,  yellow  rays  at  1300°,  blue  rays 
at  1500°,  and  white  light  at  2000°.  It  is  found, 
however,  that  as  the  temperature  of  a  wire  is 
pushed  beyond  this  figure  the  light  emitted  be- 
comes far  more  brilliant  than  the  increase  of 
temperature  would  seem  to  warrant.  It  there- 
fore pays  to  elevate  the  temperature  of  the  fila- 
ment as  high  as  possible.  Unfortunately  the 
most  refractory  metals,  such  as  platinum  and  al- 
loys of  platinum  with  iridium,  fuse  at  a  tempera- 
ture of  about  3450°  Fahrenheit.  Electricians  have 
therefore  forsaken  metals,  and  fallen  back  on 
carbon  for  producing  a  light.  In  1845  Mr.  Staite 
devised  an  incandescent  lamp  consisting  of  a  fine 
rod  or  stick  of  carbon  rendered  white-hot  by  the 
current,  and  to  preserve  the  carbon  from  burning 


ELECTRIC   LIGHT  AND   HEAT. 


in  the  atmosphere,  he  enclosed  it  in  a  glass  bulb, 
from  which  the  air  was  exhausted  by  an  air  pump. 
Edison  and  Swan,  in  1878,  and  subsequently,  went 
a  step  further,  and  substituted  a  filament  or  fine 
thread  of  carbon  for  the  rod.  The  new  lamp 
united  the  advantages  of  wire  in  point  of  form 
with  those  of  carbon  as  a  material.  The  Edison 
filament  was  made  by  cutting  thin  slips  of  bam- 
boo and  charring  them,  the  Swan  by  carbonising 
linen  fibre  with  sulphuric  acid.  It  was  subse- 
quently found  that  a  hard  skin  could  be  given  to 
the  filament  by  "  flashing  "  it — that  is  to  say,  heat- 
ing it  to  incandescence  by 
the  current  in  an  atmosphere 
of  hydro  -  carbon  gas.  The 
filament  thus  treated  becomes 
dense  and  resilient. 

Figure  63  represents  an 
ordinary  glow  lamp  of  the 
Edison-Swan  type,  where  E 
is  the  filament,  moulded  into 
a  loop,  and  cemented  to  two 
platinum  wires  or  electrodes 
P  penetrating  the  glass  bulb 
B,  which  is  exhausted  of  air. 

Platinum  is  chosen  be- 
cause it  expands  and  con- 
tracts with  temperature  about 
the  same  as  glass,  and  hence 
there  is  little  chance  of  the 
glass  cracking  through  unequal  stress.  The  vac- 
uum in  the  bulb  is  made  by  a  mercurial  air  pump 
of  the  Sprengel  sort,  and  the  pressure  of  air  in  it 
is  only  about  one-millionth  of  an  atmosphere. 
The  bulb  is  fastened  with  a  holder  like  that 
shown  in  figure  64,  where  two  little  hooks  //"con- 


8 


FIG.  63. 


n6 


THE   STORY  OF  ELECTRICITY. 


FIG.  64. 


nected  to  screw  terminals  T  T  are  provided  to 
make  contact  with  the  platinum  terminals  of  the 
lamp  (P,  figure  63),  and  the  spiral 
spring,  by  pressing  on  the  bulb,  en- 
sures a  good  contact. 

Fig.  65  is  a  cut  of  the  ordinary 
Edison  lamp  and  socket.  One  end 
of  the  filament  is  connected  to  the 
metal  screw  ferule  at  the  base. 
The  other  end  is  attached  to  the 
metal  button  in  the  centre  of  the 
extreme  bottom  of  the  base. 
Screwing  the  lamp 
into  the  socket  au- 
tomatically connects  the  filament 
on  one  end  to  the  screw,  on  the 
other  to  an  insulated  plate  at  the 
bottom  of  the  socket. 

The  resistance  of  such  a  fila- 
ment hot  is  about  200  ohms,  and 
to  produce  a  good  light  from  it 
the  battery  or  dynamo  ought  to 
give  an  electromotive  force  of  at 
least  100  volts.  Few  voltaic 
cells  or  accumulators  have  an 
electromotive  force  of  more  than 
2  volts,  therefore  we  require  a 
battery  of  50  cells  joined  in  se- 
ries, each  cell  giving  2  volts,  and 
the  whole  set  100  volts.  The 
strength  of  current  in  the  circuit 
must  also  be  taken  into  account. 
To  yield  a  good  light  such  a 
lamp  requires  or  "  takes  "  about 
£  an  ampere.  Hence  the  cells 
must  be  chosen  with  regard  to  FIG.  65. 


ELECTRIC   LIGHT  AND   HEAT.  117 

their  size  and  internal  resistance  as  well  as  to 
their  kind,  so  that  when  the  battery,  in  series,  is 
connected  to  the  lamp,  the  resistance  of  the  whole 
circuit,  including  the  filament  or  lamp,  the  battery 
itself,  and  the  connecting  wires  shall  give  by 
Ohm's  law  a  current  of  \  an  ampere.  It  will  be  un- 
derstood that  the  current  has  the  same  strength 
in  every  part  of  the  circuit,  no  matter  how  it  is 
made  up.  Thus,  if  £  of  an  ampere  is  flowing  in 
the  lamp,  it  is  also  flowing  in  the  battery  and 
wires.  An  Edison-Swan  lamp  of  this  model  gives 
a  light  of  about  15  candles,  and  is  well-adapted 
for  illuminating  the  interior  of  houses.  The  tem- 
perature of  the  carbon  filament  is  about  3450° 
Fahr. — that  is  to  say,  the  temperature  at  which 
platinum  melts.  Similar  lamps  of  various  sizes 
and  shapes  are  also  made,  some  equivalent  to  as 
many  as  100  candles,  and  fitted  for  large  halls 
or  streets,  others  emitting  a  tiny  beam  like  the 
spark  of  a  glow-worm,  and  designed  for  medical 
examinations,  or  lighting  flowers,  jewels,  and 
dresses  in  theatres  or  ball-rooms. 

The  electric  incandescent  lamp  is  pure  and 
healthy,  since  it  neither  burns  nor  pollutes  the 
air.  It  is  also  cool  and  safe,  for  it  produces 
little  heat,  and  cannot  ignite  any  inflammable 
stuffs  near  it.  Hence  its  peculiar  merit  as  a 
light  for  colliers  working  in  fiery  mines.  Inde- 
pendent of  air,  it  acts  equally  well  under  water, 
and  is  therefore  used  by  divers.  Moreover,  it 
can  be  fixed  wherever  a  wire  can  be  run,  does 
not  tarnish  gilding,  and  lends  itself  to  the  most 
artistic  decoration. 

Electric  lamps  are  usually  connected  in  circuit 
on  the  series,  parallel,  and  three-wire  system. 

The  series  system  is  shown  in  figure  66,  where 


n8 


THE   STORY  OF   ELECTRICITY. 


the  lamps  L  L  follow  each  other  in  a  row  like 
beads  on  a  string.     It  is  commonly  reserved  for 


FIG.  66. 

the  arc  lamp,  which  has  a  resistance  so  low  that 
a  moderate  electromotive  force  can  overcome  the 
added  resistance  of  the  lamps,  but,  of  course,  if 


FIG.  67. 

the  circuit  breaks  at  any  point  all  the  lamps  go 
out. 

The  parallel  system  is  illustrated  in  figure  67, 
where  the  lamps  are  connected  between  two  main 
conductors  cross-wise,  like  the  steps  of  a  ladder. 
The  current  is  thus  divided  into  cross  channels, 
like  water  used  for  irrigating  fields,  and  it  is  ob- 
vious that,  although  the  circuit  is  broken  at  one 
point,  say  by  the  rupture  of  a  filament,  all  the 
lamps  do  not  go  out. 


ELECTRIC   LIGHT  AND   HEAT. 


Fig.  68  exhibits  the  Edison  three-wire  system, 
in  which  two  batteries  or  dynamos  are  connected 


X- 


FIG.  68. 

together  in  series,  and  a  third  or  central  main 
conductor  is  run  from  their  middle  poles.  The  plan 
saves  a  return  wire,  for  if  two  generators  had 
been  used  separately,  four  mains  would  have  been 
necessary. 

The  parallel  and  three-wire  systems  in  various 
groups,  with  or  without  accumulators  as  local 
reservoirs,  are  chiefly  employed  for  incandescent 
lamps. 

The  main  conductors  conveying  the  current 
from  the  dynamos  are  commonly  of  stout  copper 
insulated  with  air  like  telegraph  wires,  or  cables 
coated  with  india-rubber  or  gutta-percha,  and 
buried  underground  or  suspended  overhead. 
The  branch  and  lamp  conductors  or  "leads"  are 
finer  wires  of  copper,  insulated  with  india-rubber 
or  silk. 

The  current  of  an  installation  or  section  of 
one  is  made  and  broken  at  will  by  means  of  a 
"  switch  "  or  key  turned  by  hand.  It  is  simply  a 


I2O 


THE  STORY  OF  ELECTRICITY. 


series  of  metal  contacts  insulated  from  each  other 
and  connected  to  the  conductors,  with  a  sliding 
contact  connected  to  the  dynamo  which  travels 
over  them.  To  guard  against  an  excess  of  cur- 
rent on  the  lamps,  "  cut-outs,"  or  safety-fuses,  are 
inserted  between  the  switch  and  the  conductors, 
or  at  other  leading  points  in  the  circuit.  They 
are  usually  made  of  short  slips  of  metal  foil  or 
wire,  which  melt  or  deflagrate  when  the  current 
is  too  strong,  and  thus  interrupt  the  circuit. 


FIG.  69.— Electrical  Phosphorescence. 

There  is  some  prospect  of  the  luminosity  ex- 
cited in  a  vacuum  tube  by  the  alternating  currents 
from  a  dynamo  or  an  induction  coil  becoming 
an  illuminant.  Crookes  has  obtained  exquisitely 
beautiful  glows  by  the  phosphorescence  of  gems 


ELECTRIC   LIGHT  AND   HEAT.  121 

and  other  minerals  in  a  vacuum  bulb  like  that 
shown  in  figure  69,  where  A  and  B  are  the  metal 
electrodes  on  the  outside  of  the  glass.  A  heap  of 
diamonds  from  various  countries  emit  red,  orange, 
yellow,  green,  and  blue  rays.  Ruby,  sapphire, 
and  emerald  give  a  deep  red,  crimson,  or  lilac 
phosphorescence,  and  sulphate  of  zinc  a  magnifi- 
cent green  glow.  Tesla  has  also  shown  that 
vacuum  bulbs  can  be  lit  inside  without  any  out- 
side connection  with  the  current,  by  means  of  an 
apparatus  like  that  shown  in  figure  70,  where  D 
is  an  alternating  dynamo,  C  a  condenser,  P  S  the 
primary  and  secondary  coils  of  a  sparking  trans- 
former, T  T  two  metal  sheets  or  plates,  and  B  B 
the  exhausted  bulbs.  The  alternating  or  see-saw 


r         B  ft  r 

FIG.  70. — The  Ideal  Illuminant 

current  in  this  case  charges  the  condenser  and 
excites  the  primary  coil  P,  while  the  induced  cur- 
rent in  the  secondary  coil  S  charges  the  terminal 
plates  T  T.  So  long  as  the  bulbs  or  tubes  are 
kept  within  the  space  between  the  plates,  they 
are  filled  with  a  soft  radiance,  and  it  is  easy  to 


THE  STORY  OF  ELECTRICITY. 


see  that  if  these  plates  covered  the  opposite  walls 
of  a  room,  the  vacuum  lamps  would  yield  a  light 
in  any  part  of  it. 

Electric  heating  bids  fair  to  become  almost  as 
important  as  electric  illumination.     When  the  arc 
was  first  discovered  it  was  noticed  that  platinum, 
gold,    quartz,    ruby,    and   diamond — in   fine,   the 
most  refractory  minerals — were  melted  in  it,  and 
ran  like  wax.     Ores  and  salts  of  the  metals  were 
also  vapourised,  and  it  was  clear  that  a  powerful 
engine  of  research  had  been  placed  in  the  hands 
of  the  chemist.    As  a  matter  of  fact,  the  tempera- 
ture of   the  carbons 
in    the    arc   is   com- 
parable   to    that    of 
the   Sun.      It    meas- 
ures 5000  to  10,000° 
Fahrenheit,    and    is 
the      highest     artifi- 
cial heat  known.    Sir 
William  Siemens  was 
among    the    first    to 
make  an  electric  fur- 
nace   heated   by  the 
arc,  which  fused  and 

vapourised  metallic  ores,  so  that  the  metal  could 
be  extracted  from  them.  Aluminium,  chromium, 
and  other  valuable  metals  are  now  smelted  by  its 
means,  and  rough  brilliants  such  as  those  found 
in  diamond  mines  and  meteoric  stones  have  been 
crystallised  from  the  fumes  of  carbon,  like  hoar 
frost  in  a  cold  mist. 

The  electric  arc  is  also  applied  to  the  welding 
of  wires,  boiler  plates,  rails,  and  other  metal  work, 
by  heating  the  parts  to  be  joined  and  fusing  them 
together. 


FIG.  71. 


ELECTRIC   LIGHT  AND   HEAT. 


123 


Cooking  and  heating  by  electricity  are  coming 
more  and  more  into  favour,  owing  to  their  clean- 


FIG.  72. 


FIG.  73. 


liness  and  convenience.     Kitchen  ranges,  includ- 
ing ovens  and  grills,  entirely  heated  by  the  elec- 
tric current,  are  finding 
their  way  into  the  best 
houses  and  hotels.    Most 
of  these  are  based 
on   the    principle 
of  incandescence, 
the  current  heat- 
ing a  fine  wire  or 
other    conductor 
of     high 4    resist- 
ance   in    passing 
through  it.     Fig- 
ure 71  represents  an  elec- 
tric kettle  of    this  sort, 
which    requires  no    out- 
side fire  to  boil  it,  since 
the  current  flows  through 
fine  wires  of  platinum  or 
some      highly     resisting 
metal  embedded  in  fire- 
FIG.  74.  proof  insulating  cement 

in  its  bottom.     Figures 
72  and  73  are  a  sauce-pan  and  a  flat-iron  heated 


124 


THE   STORY  OF   ELECTRICITY. 


in  the  same  way.     Figure  74  is  a  cigar-lighter  for 
smoking  rooms,  the  fusee  f  consisting  of  short 
platinum  wires,   which  be- 
come   red-hot    when    it    is 
unhooked,  and  at  the  same 
time   the   lamp  L  is  auto- 
matically lit.     Figure  75  is 
an     electric     radiator     for 
heating   rooms   and  passa- 
ges,   after    the    manner   of 
stoves  and  hot  water  pipes. 
Quilts  for  beds,  warmed 
by    fine    wires    inside, 
have  also  been  brought 
out,  a  constant  temper- 
ature being  maintained 
by  a  simple  regulator, 
and   it   is   not   unlikely 
that   personal  clothing 

of  the  kind  will  soon  be  at  the  service  of  invalids 
and  chilly  mortals,  more  especially  to  make  them 
comfortable  on  their  travels. 

An  ingenious  device  places  an  electric  heater 
inside  a  hot  water  bag,  thus  keeping  it  at  a  uni- 
form temperature  for  sick-room  and  hospital  use. 


FIG.  75. 


CHAPTER  VIII. 

ELECTRIC    POWER. 

ON  the  discovery  of  electromagnetism  (Chap. 
IV.),  Faraday,  Barlow,  and  others  devised  ex- 
perimental apparatus  for  producing  rotary  motion 
from  the  electric  current,  and  in  1831,  Joseph 


ELECTRIC   POWER.  125 

Henry,  the  famous  American  electrician,  invented 
a  small  electromagnetic  engine  or  motor!  These 
early  machines  were  actuated  by  the  current  from 
a  voltaic  battery,  but  in  the  middle  of  the  century 
Jacobi  found  that  a  dynamo-electric  generator 
can  also  work  as  a  motor,  and  that  by  coupling 
two  dynamos  in  circuit — one  as  a  generator,  the 
other  as  a  motor — it  was  possible  to  transmit  me- 
chanical power  to  any  distance  by  means  of  elec- 
tricity. Figure  76  is  a  diagram  of  a  simple  cir- 
cuit for  the  transmission  of  power,  where  D  is  the 


M 


FIG.  76. 


technical  symbol  for  a  dynamo  as  a  generator, 
having  its  poles  (-f  and  —  )  connected  by  wire  to 
the  poles  of  M,  the  distant  dynamo,  as  a  motor. 
The  generator  D  is  driven  by  mechanical  energy 
from  any  convenient  source,  and  transforms  it 
into  electric  energy,  which  flows  through  the  cir- 
cuit in  the  direction  of  the  arrows,  and,  in  trav- 
ersing the  motor  M,  is  re-transformed  into  me- 
chanical energy.  There  is,  of  course,  a  certain 
waste  of  energy  in  the  process,  but  with  good 
machines  and  conductors,  it  is  not  more  than  10 
to  25  per  cent.,  or  the  "  efficiency  "  of  the  instal- 
lation is  from  75  to  90  per  cent.  —  that  is  to  say, 
for  every  100  horse-power  put  into  the  generator, 
from  75  to  90  horse-power  are  given  out  again  by 
the  motor. 

It  was  not  until  1870,  when  Gramme  had  im- 
proved the  dynamo,  that  power  was  practically 


126  THE  STORY  OF  ELECTRICITY. 

transmitted  in  this  way,  and  applied  to  pumping 
water,  and  other  work.  Since  then  great  progress 
has  been  made,  and  electricity  is  now  recognised, 
not  only  as  a  rival  of  steam,  but  as  the  best 
means  of  distributing  steam,  wind,  water,  or  any 
other  power  to  a  distance,  and  bringing  it  to  bear 
on  the  proper  point. 

The  first  electric  railway,  or,  rather,  tramway, 
was  built  by  Dr.  Werner  von  Siemens  at  Berlin  in 
1879,  and  was  soon  followed  by  many  others. 
The  wheels  of  the  car  were  driven  by  an  electric 
motor  drawing  its  electricity  from  the  rails,  which 
were  insulated  from  the  ground,  and  being  con- 
nected to  the  generator,  served  as  conductors.  It 
was  found  very  difficult  to  insulate  the  rails,  and 
keep  the  electricity  from  leaking  to  the  ground, 
however,  and  at  the  Paris  Electrical  Exhibition 
of  1881,  von  Siemens  made  a  short  tramway  in 
which  the  current  was  drawn  from  a  bare  copper 
conductor  running  on  poles,  like  a  telegraph  wire, 
along  the  line. 

The  system  will  be  understood  from  figure  77, 
where  L  is  the  overhead  conductor  joined  to  the 
positive  pole  of  the  dynamo  or  generator  in  the 
power  house,  and  C  is  a  rolling  contact  or  trolley 
wheel  travelling  with  the  car  and  connected  by 
the  wire  W  to  an  electric  motor  M  under  the  car, 
and  geared  to  the  axles.  After  passing  through 
the  motor  the  current  escapes  to  the  rail  R  by  a 
brush  or  sliding  contact  C',  and  so  returns  to  the 
negative  pole  of  the  generator.  A  very  general 
way  is  to  allow  the  return  current  to  escape  to 
the  rails  through  the  wheels.  Many  tramways, 
covering  thousands  of  miles,  are  now  worked 
on  this  plan  in  the  United  States.  At  Bangor, 
Maine,  a  modification  of  it  is  in  use  whereby  the 


ELECTRIC   POWER. 


127 


conductor  is  divided  into  sections,  alternately 
connected  to  the  positive  and  negative  poles  of 
two  generators,  coupled  together  as  in  the  "  three- 
wire  system"  of  electric  lighting  (page  119), 


FIG.  77.— An  Electric  Railway. 

their  middle  poles  being  joined  to  the  earth — that 
is  to  say,  the  rails.  It  enables  two  cars  to  be  run 
on  the  same  line  at  once,  and  with  a  considerable 
saving  of  copper. 

To  make  the  car  independent  of  the  conductor 
L  for  a  short  time,  as  in  switching,  a  battery  of 
accumulators  B  may  be  added  and  charged  from 
the  conductor,  so  that  when  the  motor  is  discon- 
nected from  the  conductor,  the  discharge  from  the 
accumulator  may  still  work  it  and  drive  the  wheels. 

Attempts  have  been  made  to  run  tramcars 
with  the  electricity  supplied  by  accumulators 
alone,  but  the  system  is  not  economical  owing  to 
the  dead  weight  of  the  cells,  and  the  periodical 
trouble  of  recharging  them  at  the  generating  sta- 
tion. 


128  THE  STORY  OF  ELECTRICITY. 

On  heavy  railroads  worked  by  electricity  the 
overhead  conductor  is  replaced  by  a  third  rail 
along  the  middle  of  the  track,  and  insulated  from 
the  ground.  In  another  system  the  middle  con- 
ductor is  buried  underground,  and  the  current  is 
tapped  at  intervals  by  the  motor  connecting  with 
it  for  a  moment  by  means  of  spring  contacts  as 
the  car  travels.  In  each  case,  however,  the  outer 
rails  serve  as  the  return  conductors. 

Another  system  puts  one  or  both  the  conduc- 
tors in  a  conduit  underground,  the  trolley  pole 
entering  through  a  narrow  slot  similar  to  that 
used  on  cable  roads. 

The  first  electric  carriages  for  ordinary  roads 
were  constructed  in  1889  by  Mr.  Magnus  Volk  of 
Brighton.  Figure  78  represents  one  of  these 
made  for  the  Sultan  of  Turkey,  and  propelled  by 
a  one-horse-power  Immisch  electric  motor,  geared 
to  one  of  the  hind  wheels  by  means  of  a  chain. 
The  current  for  the  motor  was  supplied  by  thirty 
"  E.  P.  S."  accumulators  stowed  in  the  body  of  the 
vehicle,  and  of  sufficient  power  to  give  a  speed  of 
ten  miles  an  hour.  The  driver  steers  with  a  hand 
lever  as  shown,  and  controls  the  speed  by  a  switch 
in  front  of  him. 

Vans,  bath  chairs,  and  tricycles  are  also  driven 
by  electric  motors,  but  the  weight  of  the  battery 
is  a  drawback  to  their  use. 

In  or  about  the  year  1839,  Jacobi  sailed  an 
electric  boat  on  the  Neva,  with  the  help  of  an 
electromagnetic  engine  of  one  horse-power,  fed 
by  the  current  from  a  battery  of  Grove  cells,  and 
in  1882  a  screw  launch,  carrying  several  passen- 
gers, and  propelled  by  an  electric  motor  of  three 
horse-power,  worked  by  forty-five  accumulators, 
was  tried  on  the  Thames.  Being  silent  and 


ELECTRIC   POWER. 


129 


smokeless  in   its  action,  the  electric  boat  soon 
came  into  favour,  and  there  is  now  quite  a  flotilla 


FIG.  78.— An  Electric  Carriage. 

on  the  river,  with  power  stations  for  charging 
the  accumulators  at  various  points  along  the 
banks. 

Figure  79  illustrates  the  interior  of  a  hand- 
some electric  launch,  the  Lady  Cooper,  built  for 
the  "E.  P.  S.,"  or  Electric  Power  Storage  Com- 
pany. An  electric  motor  in  the  after  part  of  the 
hull  is  coupled  directly  to  the  shaft  of  the  screw 
propeller,  and  fed  by  "  E.  P.  S."  accumulators  in 
teak  boxes  lodged  under  the  deck  amidships. 
The  screw  is  controlled  by  a  switch,  and  the 
rudder  by  an  ordinary  helm.  The  cabin  is  seven 
feet  long,  and  lighted  by  electric  lamps.  Alarm 


130  THE  STORY  OF  ELECTRICITY. 

signals  are  given  by  an  electric  gong,  and  a 
search-light  can  be  brought  into  operation  when- 
ever it  is  desirable.  The  speed  attained  by  the 
Lady  Cooper  is  from  ten  to  fifteen  knots. 

M.  Goubet,  a  Frenchman,  has  constructed  a 
submarine  boat   for  discharging   torpedoes   and 


FlG.  79. — An  Electric  Launch. 

exploring  the  sea  bottom,  which  is  propelled  by 
a  screw  and  an  electric  motor  fed  by  accumula- 
tors. It  can  travel  entirely  under  water,  below 
the  agitation  of  the  waves,  where  sea-sickness  is 
impossible,  and  the  inventor  hopes  that  vessels 
of  the  kind  will  yet  carry  passengers  across  the 
Channel. 

The  screw  propeller  of  the  Edison  and  Sim's 
torpedo  is  also  driven  by  an  electric  motor.  In 
this  case  the  current  is  conveyed  from  the  ship 
or  fort  which  discharges  the  torpedo  by  an  in- 
sulated conductor  running  off  a  reel  carried  by 
the  torpedo,  the  "  earth  "  or  return  half  of  the 
circuit  being  the  sea-water. 

All  sorts  of  machinery  are  now  worked  by  the 
electric  motor — for  instance,  cranes,  elevators, 
capstans,  rivetters,  lathes,  pumps,  chaff-cutters, 
and  saws.  Of  domestic  appliances,  figure  80 
shows  an  air  propeller  or  ventilation  fan,  where 
F  is  a  screw-like  fan  attached  to  the  spindle  of 
the  motor  M,  and  revolving  with  its  armature. 
Figure  81  represents  a  Trouve  motor  working  a 
sewing-machine,  where  N  is  the  motor  which  gears 


ELECTRIC   POWER. 


with  P  the  driving  axle  of  the  machine.  Figure 
82  represents  a  fine  drill  actuated  by  a  Griscom 
motor.  The  motor  Afis  sus- 
pended from  a  bracket  ABC 
by  the  tackle  D  Ey  and  trans- 
mits the  rotation  of  its  arm- 
ature by  a  flexible  shaft  S  T 
to  the  terminal 
drill  <9,  which  can 
be  applied  at  any 
point,  and  is  use- 
ful in  boring  teeth. 
Now  that  elec- 
tricity is  manufac- 
tured and  distrib- 
uted in  towns  and 
villages  for  the 
electric  light,  it  is 
more  and  more  employed  for 
driving  the  lighter  machine- 
ry. Steam,  however,  is  more 
economical  on  a  large  scale, 
FIG.  80.— An  Electric  Fan.  and  still  continues  to  be  used 
in  great  factories  for  the 
heavier  machinery.  Nevertheless  a  day  is  coming 
when  coal,  instead  of  being  carried  by  rail  to  dis- 
tant works  and  cities,  will  be  burned  at  the  pit 
mouth,  and  its  heat  transformed  by  means  of  en- 
gines and  dynamos  into  electricity  for  distribution 
to  the  surrounding  country.  I  have  shown  else- 
where that  peat  can  be  utilised  in  a  similar  man- 
ner, and  how  the  great  Bog  of  Allen  is  virtually  a 
neglected  gold  field  in  the  heart  of  Ireland.*  The 
sunshine  of  deserts,  and  perhaps  the  electricity  of 
the  atmosphere,  but  at  all  events  the  power  of 

*  The  Nineteenth  Century  for  December  1894. 


I32 


THE  STORY  OF  ELECTRICITY. 


winds,  waves,  and  waterfalls  are  also  destined  to 
whirl  the  dynamo,  and  yield  us  light,  heat,  or  mo- 
tion. Much  has  already  been  done  in  this  direc- 
tion. In  1891  the  power  of  turbines  driven  by  the 


FIG.  81.— An  Electric  Sewing  Machine. 

Falls  of  Neckar  at  Lauffen  was  transformed  into 
electricity,  and  transmitted  by  a  small  wire  to  the 
Electrical  Exhibition  of  Frankfort-on-the-Main, 
117  miles  away.  The  city  of  Rome  is  now  lighted 
from  the  Falls  of  Tivoli,  16  miles  distant.  The 
finest  cataract  in  Great  Britain,  the  Falls  of  Foyers, 
in  the  Highlands,  which  persons  of  taste  and  cul- 
ture wished  to  preserve  for  the  nation,  is  being 
sacrificed  to  the  spirit  of  trade,  and  deprived  of 
its  waters  for  the  purpose  of  generating  electricity 
to  reduce  aluminium  from  its  ores. 

The  great  scheme  recently  completed  for  util- 
izing the  power  of  Niagara  Falls  by  means  of 
electricity  is  a  triumph  of  human  enterprise  which 


POWER. 


133 


outrivals   some    of    the   bold   creations   of   Jules 
Verne. 

When  in  1678  the  French  missionaries  La  Salle 
and  Hennepin  discovered  the  stupendous  cataract 
on  the  Niagara  River 
between   Lake  Onta- 

rio   and    Lake    Erie,  ^ 

the  science  of  elec-  "=* 
tricity  was  in  its  ear- 
ly infancy,  and  little 
more  was  known 
about  the  mysterious 
force  which  is  per- 
forming miracles  in 
our  day  than  its  man- 
ifestation on  rubbed 
amber,  sealing-wax, 
glass,  and  other  bod- 
ies. Nearly  a  hun- 
dred years  had  still 
to  pass  ere  Franklin 
should  demonstrate 
the  identity  of  the  electric  fire  with  lightning,  and 
nearly  another  hundred  before  Faraday  should 
reveal  a  mode  of  generating  it  from  mechanical 
power.  Assuredly,  neither  La  Salle  nor  his  con- 
temporaries ever  dreamed  of  a  time  when  the 
water-power  of  the  Falls  would  be  distributed  by 
means  of  electricity  to  produce  light  or  heat  and 
serve  all  manner  of  industries  in  the  surrounding 
district.  The  awestruck  Iroquois  Indians  had 
named  the  cataract  "  Oniagahra,"  or  Thunder  of 
the  Waters,  and  believed  it  the  dwelling-place  of 
the  Spirit  of  Thunder.  This  poetical  name  is 
none  the  less  appropriate  now  that  the  modern 
electrician  is  preparing  to  draw  his  lightnings  from 


FIG.  82. — An  Electric  Drill. 


134  THE  STORY  OF    ELECTRICITY. 

its  waters  and  compel  the  genius  loci  to  become 
his  willing  bondsman. 

The  Falls  of  Niagara  are  situated  about 
twenty-one  miles  from  Lake  Erie,  and  fourteen 
miles  from  Lake  Ontario.  At  this  point  the  Ni- 
agara River,  nearly  a  mile  broad,  flowing  between 
level  banks,  and  parted  by  several  islands,  is  sud- 
denly shot  over  a  precipice  170  feet  high,  and 
making  a  sharp  bend  to  the  north,  pursues  its 
course  through  a  narrow  gorge  towards  Lake  On- 
tario. The  Falls  are  divided  at  the  brink  by  Goat 
Island,  whose  primeval  woods  are  still  thriving  in 
their  spray.  The  Horseshoe  Fall  on  the  Canadian 
side  is  812  yards,  and  the  American  Falls  on  the 
south  side  are  325  yards  wide.  For  a  consider- 
able distance  both  above  and  below  the  Falls  the 
river  is  turbulent  with  rapids. 

The  water-power  of  the  cataract  has  been  em- 
ployed from  olden  times.  The  French  fur-traders 
placed  a  mill  beside  the  upper  rapids,  and  the 
early  British  settlers  built  another  to  saw  the  tim- 
ber used  in  their  stockades.  By-and-by,  the 
Stedman  and  Porter  mills  were  established  below 
the  Falls;  and  subsequently,  others  which  derived 
their  water-supply  from  the  lower  rapids  by  means 
of  raceways  or  leads.  Eventually,  an  open  hy- 
draulic can-al,  three-fourths  of  a  mile  long,  was 
cut  across  the  elbow  of  land  on  the  American 
side,  through  the  town  of  Niagara  Falls,  between 
the  rapids  above  and  the  verge  of  the  chasm  below 
the  Falls,  where,  since  1874,  a  cluster  of  factories 
has  arisen,  which  discharge  their  spent  water  over 
the  cliff  in  a  series  of  cascades  almost  rivalling 
Niagara  itself.  This  canal,  which  only  taps  a 
mere  drop  from  the  ocean  of  power  that  is  run- 
ning to  waste,  has  been  utilised  to  the  full ; 


ELECTRIC  POWER.  135 

the  decrease  of  water-privileges  in  the  New  Eng- 
land States,  owing  to  the  clearing  of  the  forests 
and  settlement  of  the  country,  together  with  the 
growth  of  the  electrical  industries,  have  led  to  a 
further  demand  on  the  resources  of  Niagara. 

With  the  example  of  Minneapolis,  which  draws 
the  power  for  its  many  mills  from  the  Falls  of  St. 
Anthony,  in  the  Mississippi  River,  before  them,  a 
group  of  far-seeing  and  enterprising  citizens  of 
Niagara  Falls  resolved  to  satisfy  this  requirement 
by  the  foundation  of  an  industrial  city  in  the 
neighbourhood  of  the  Falls.  They  perceived  that 
a  better  site  could  nowhere  be  found  on  the 
American  Continent.  Apart  from  its  healthy  air 
and  attractive  scenery,  Niagara  is  a  kind  of  half- 
way house  between  the  East  and  West,  the  con- 
suming and  the  producing  States.  By  the  Erie 
Canal  at  Tonawanda  it  commands  the  great  water- 
way of  the  Lakes  and  the  St.  Lawrence.  A  sys- 
tem of  trunk  railways  from  different  parts  of  the 
States  and  Canada  are  focussed  there,  and  cross 
the  river  by  the  Cantilever  and  Suspension  bridges 
below  the  Falls.  The  New  York  Central  and 
Hudson  River,  the  Lehigh  Valley,  the  Buffalo, 
Rochester,  and  Pittsburgh,  the  Michigan  Central, 
and  the  Grand  Trunk  of  Canada,  are  some  of  these 
lines.  Draining  as  it  does  the  great  lakes  of  the 
interior,  which  have  a  total  area  of  92,000  square 
miles,  with  an  aggregate  basin  of  290,000  square 
miles,  the  volume  of  water  in  the  Niagara  River 
passing  over  the  cataract  every  second  is  some- 
thing like  300,000  cubic  feet ;  and  this,  with  a  fall 
of  276  feet  from  the  head  of  the  upper  rapids  to 
the  whirlpool  rapids  below,  is  equivalent  to  about 
nine  million,  or,  allowing  for  waste  in  the  turbines, 
say,  seven  million  horse-power.  Moreover,  the 


136  THE   STORY   OF   ELECTRICITY. 

great  lakes  discharging  into  each  other  form  a 
chain  of  immense  reservoirs,  and  the  level  of  the 
river  being  little  affected  by  flood  or  drought,  the 
supply  of  pure  water  is  practically  constant  all 
the  year  round.  Mr.  R.  C.  Reid  has  shown  that 
a  rainfall  of  three  inches  in  twenty-four  hours 
over  the  basin  of  Lake  Superior  would  take 
ninety  days  to  run  off  into  Lake  Huron,  which, 
with  Lake  Michigan,  would  take  as  long  to  over- 
flow into  Lake  Erie  ;  and,  therefore,  six  months 
would  elapse  before  the  full  effect  of  the  flood 
was  expended  at  the  Falls. 

x  The  first  outcome  of  the  movement  was  the 
Niagara  River  Hydraulic  Power  and  Sewer  Com- 
pany, incorporated  in  1886,  and  succeeded  by  the 
Niagara  Falls  Power  Company.  The  old  plan  of 
utilising  the  water  by  means  of  an  open  canal  was 
unsuited  to  the  circumstances,  and  the  company 
adopted  that  of  the  late  Mr.  Thomas  Evershed, 
divisional  engineer  of  the  New  York  State  Canals. 
Like  the  other,  it  consists  in  tapping  the  river 
above  the  Falls,  and  using  the  pressure  of  the 
water  to  drive  the  number  of  turbines,  then  re- 
storing the  water  to  the  river  below  the  Falls ; 
but  instead  of  a  surface  canal,  the  tail-race  is  a 
hydraulic  tunnel  or  underground  conduit.  To  this 
end  some  fifteen  hundred  acres  of  spare  land, 
having  a  frontage  just  above  the  upper  rapids,  was 
quietly  secured  at  the  low  price  of  three  hundred 
dollars  an  acre;  and  we  believe  its  rise  in  value 
owing  to  the  progress  of  the  works  is  such  that 
a  yearly  rental  of  two  hundred  dollars  an  acre  can 
even  now  be  got  for  it.  This  land  has  been  laid 
out  as  an  industrial  city,  with  a  residential  quar- 
ter for  the  operatives,  wharves  along  the  river, 
and  sidings  or  short  lines  to  connect  with  the 


ELECTRIC   POWER.  137 

trunk  railways.  In  carrying  out  their  purpose 
the  company  has  budded  and  branched  into  other 
companies — one  for  the  purchase  of  the  land  ; 
another  for  making  the  railways;  and  a  third, 
the  Cataract  Construction  Company,  which  is 
charged  with  the  carrying  out  of  the  engineer- 
ing works,  for  the  utilisation  of  the  water-power, 
and  is  therefore  the  most  important  of  all.  A 
subsidiary  company  has  also  been  formed  to 
transmit  by  electricity  a  portion  of  the  available 
power  to  the  city  of  Buffalo,  at  the  head  of  the 
Niagara  River,  on  Lake  Erie,  some  twenty  miles 
distant.  All  these  affiliated  bodies  are,  however, 
under  the  directorate  of  the  Cataract  Construc- 
tion Company ;  and  amongst  those  who  have 
taken  the  most  active  part  in  the  work  we  may 
mention  the  president,  Mr.  E.  D.  Adams;  Pro- 
fessor Coleman  Sellers,  the  consulting  engineer  ; 
and  Professor  George  Forbes,  F.  R.  S.,  the  con- 
sulting electrical  engineer,  a  son  of  the  late  Prin- 
cipal Forbes  of  Edinburgh. 

In  securing  the  necessary  right  of  way  for  the 
hydraulic  tunnel  or  in  the  acquisition  of  land, 
the  Company  has  shown  consummate  tact.  A 
few  proprietors  declined  to  accept  its  terms,  and 
the  Company  selected  a  parallel  route.  Having 
obtained  the  right  of  way  for  the  latter,  it  in- 
formed the  refractory  owners  on  the  first  line  of 
their  success,  and  intimated  that  the  Company 
could  now  dispense  with  that.  On  this  the 
sticklers  professed  their  willingness  to  accept 
the  original  terms,  and  the  bargain  was  con- 
cluded, thus  leaving  the  Company  in  possession 
of  the  rights  of  way  for  two  tunnels,  both  of 
which  they  propose  to  utilise. 

The  liberal  policy  of  the  directors  is  deserving 


138  THE  STORY  OF  ELECTRICITY. 

of  the  highest  commendation.  They  have  risen 
above  mere  u  chauvinism,"  and  instead  of  nar- 
rowly confining  the  work  to  American  engineers, 
they  have  availed  themselves  of  the  best  scientific 
counsel  which  the  entire  world  could  afford.  The 
great  question  as  to  the  best  means  of  distribut- 
ing and  applying  the  power  at  their  command 
had  to  be  settled  ;  and  in  1890,  after  Mr.  Adams 
and  Dr.  Sellers  had  made  a  visit  of  inspection 
to  Europe,  an  International  Commission  was  ap- 
pointed to  consider  the  various  methods  sub- 
mitted to  them,  and  award  prizes  to  the  success- 
ful competitors.  Lord  Kelvin  (then  Sir  William 
Thomson)  was  the  president,  and  Professor  W. 
C.  Unwin,  the  well-known  expert  in  hydraulic 
engineering,  the  secretary,  while  other  members 
were  Professor  Mascart  of  the  Institute,  a  lead- 
ing French  electrician ;  Colonel  Turretini  of 
Geneva,  and  Dr.  Sellers.  A  large  number  of 
schemes  were  sent  in,  and  many  distinguished 
engineers  gave  evidence  before  the  Commission. 
The  relative  merits  of  compressed  air  and  elec- 
tricity as  a  means  of  distributing  the  power  were 
discussed,  and  on  the  whole  the  balance  of  opinion 
was  in  favour  of  electricity.  Prizes  of  two  hun- 
dred and  two  hundred  and  fifty  pounds  were 
awarded  to  a  number  of  firms  who  had  submitted 
plans,  but  none  of  these  were  taken  up  by  the 
Company.  The  impulse  turbines  of  Messrs. 
Faesch  &  Piccard,  of  Geneva,  who  gained  a  prize 
of  two  hundred  and  fifty  pounds,  have,  however, 
been  adopted  since.  It  is  another  proof  of  the 
determination  of  the  Company  to  procure  the 
best  information  on  the  subject,  regardless  of 
cost,  that  Professor  Forbes  had  carte  blanche  to 
go  to  any  part  of  the  world  and  make  a  report 


ELECTRIC  POWER.  139 

on  any  system  of  electrical  distribution  which  he 
might  think  fit. 

With  the  selection  of  electricity  another  ques- 
tion arose  as  to  the  expediency  of  employing 
continuous  or  alternating  currents.  At  that  time 
continuous  currents  were  chiefly  in  vogue,  and  it 
speaks  well  for  the  sagacity  and  prescience  of 
Professor  Forbes  that  he  boldly  advocated  the 
adoption  of  alternating  currents,  more  especially 
for  the  transmission  of  power  to  Buffalo.  His 
proposals  encountered  strong  opposition,  even  in 
the  highest  quarters ;  but  since  then,  partly 
owing  to  the  striking  success  of  the  Lauffen  to 
Frankfort  experiment  in  transmitting  power  by 
alternating  currents  over  a  bare  wire  on  poles 
a  distance  of  more  than  a  hundred  miles,  the 
directors  and  engineers  have  come  round  to  his 
view  of  the  matter,  and  alternating  currents  have 
been  employed,  at  all  events  for  the  Buffalo  line, 
and  also  for  the  chief  supply  of  the  industrial 
city.  Continuous  currents,  flowing  always  in  the 
same  direction,  like  the  current  of  a  battery,  can, 
it  is  true,  be  stored  in  accumulators,  but  they 
cannot  be  converted  to  higher  or  lower  pressure 
in  a  transformer.  Alternating  currents,  on  the 
other  hand,  which  see-saw  in  direction  many 
times  a  second,  cannot  be  stored  in  accumulators, 
but  they  can  be  sent  at  high  pressure  along  a  very 
fine  wire,  and  then  converted  to  higher  or  lower 
pressures  where  they  are  wanted,  and  even  to  con- 
tinuous currents.  Each  kind,  therefore,  has  its 
peculiar  advantages,  and  both  will  be  employed 
to  some  extent. 

With  regard  to  the  engineering  works,  the 
hydraulic  tunnel  starts  from  the  bank  of  the 
river  where  it  is  navigable,  at  a  point  a  mile  and 


140  THE  STORY   OF   ELECTRICITY. 

a  half  above  the  Falls,  and  after  keeping  by  the 
shore,  it  cuts  across  the  bend  beneath  the  city  of 
Niagara  Falls,  and  terminates  below  the  Suspen- 
sion Bridge  under  the  Falls  at  the  level  of  the 
water.  It  is  6700  yards  long,  and  of  a  horseshoe 
section,  19  feet  wide  by  21  feet  high.  It  has  been 
cut  160  feet  below  the  surface  through  the  lime- 
stone and  shale,  but  is  arched  with  brick,  having 
rubble  above,  and  at  the  outfall  is  lined  on  the 
invert  or  under  side  with  iron.  The  gradient  is 
36  feet  in  the  mile,  and  the  total  fall  is  205  feet,  of 
which  140  feet  are  available  for  use.  The  capac- 
ity of  the  tunnel  is  100,000  horse-power.  In  the 
lands  of  the  company  it  is  400  feet  from  the  mar- 
gin of  the  river,  to  which  it  is  connected  by  a 
canal,  which  is  over  1500  feet  long,  500  feet  wide 
at  the  mouth,  and  12  feet  deep. 

Out  of  this  canal,  head-races  fitted  with  sluices 
conduct  the  water  to  a  number  of  wheel-pits  160 
feet  deep,  which  have  been  dug  near  the  edge  of 
the  canal,  and  communicate  below  with  the  tun- 
nel. At  the  bottom  of  each  wheel-pit  a  5000 
horse-power  Girard  double  turbine  is  mounted  on 
a  vertical  shaft,  which  drives  a  propeller  shaft 
rising  to  the  surface  of  the  ground  ;  a  dynamo  of 
5000  horse-power  is  fixed  on  the  top  of  this  shaft, 
and  so  driven  by  it.  The  upward  pressure  of  the 
water  is  ingeniously  contrived  to  relieve  the 
foundation  of  the  weight  of  the  turbine  shaft  and 
dynamo.  Twenty  of  these  turbines,  which  are 
made  by  the  I.  P.  Morris  Company  of  Philadel- 
phia, from  the  designs  of  Messrs.  Faesch  and 
Piccard,  will  be  required  to  utilize  the  full  capac- 
ity of  the  tunnel. 

The  company  possesses  a  strip  of  land  extend- 
ing two  miles  along  the  shore  j  and  in  excavating 


ELECTRIC   POWER.  141 

the  tunnel  a  coffer-dam  was  made  with  the  ex- 
tracted rock,  to  keep  the  river  from  flooding  the 
works.  This  dam  now  forms  part  of  a  system  by 
which  a  tract  of  land  has  been  reclaimed  from  the 
river.  Part  of  it  has  already  been  acquired  by 
the  Niagara  Paper  Pulp  Company,  which  is  build- 
ing gigantic  factories,  and  will  employ  the  tail- 
race  or  tunnel  of  the  Cataract  Construction  Com- 
pany. Wharfs  for  the  use  of  ships  and  canal 
boats  will  also  be  constructed  on  this  frontage. 
By  land  and  water  the  raw  materials  of  the  West 
will  be  conveyed  to  the  industrial  town  which  is 
now  coming  into  existence  ;  grain  from  the  prai- 
ries of  Illinois  and  Dakota;  timber  from  the  for- 
ests of  Michigan  and  Wisconsin  ;  coal  and  copper 
from  the  mines  of  Lake  Superior  ;  and  what  not. 
It  is  expected  that  one  industry  having  a  seat 
there  will  attract  others.  Thus,  the  pulp  mills 
will  bring  the  makers  of  paper  wheels  and  bar- 
rels ;  the  smelting  of  iron  will  draw  foundries 
and  engine  works ;  the  electrical  refining  of  cop- 
per will  lead  to  the  establishment  of  wire-works, 
cable  factories,  dynamo  shops,  and  so  on.  Alu- 
minum, too,  promises  to  create  an  important  in- 
dustry in  the  future.  In  the  meantime,  the  Cata- 
ract Construction  Company  is  about  to  start  an 
electrical  factory  of  its  own,  which  will  give  em- 
ployment to  a  large  number  of  men.  It  has  also 
undertaken  the  water  supply  of  the  adjacent  city 
of  Niagara  Falls.  The  Cataract  Electric  Com- 
pany of  Buffalo  has  obtained  the  exclusive  right 
to  use  the  electricity  transmitted  to  that  city, 
and  the  line  will  be  run  in  a  subway.  This 
underground  line  will  be  more  expensive  to  make 
than  an  overhead  line,  but  it  will  not  require  to 
be  renewed  every  eight  to  fifteen  years,  and  it 


142  THE   STORY  OF   ELECTRICITY. 

will  not  be  liable  to  interruption  from  the  heavy 
gales  that  sweep  across  the  lakes,  or  the  weight 
of  frozen  sleet :  moreover,  it  will  be  more  easily 
inspected,  and  quite  safe  for  the  public.  We 
should  also  add  that,  in  addition  to  the  contem- 
plated duplicate  tunnel  of  100,000  horse-power, 
the  Cataract  Construction  Company  owns  a  con- 
cession for  utilising  250,000  horse-power  from  the 
Horseshoe  Falls  on  the  Canadian  side  in  the  same 
manner.  It  has  thus  a  virtual  monopoly  of  the 
available  water-power  of  Niagara,  and  the  pro- 
moters have  not  the  least  doubt  that  the  enter- 
prise will  be  a  great  financial  success.  Already 
the  Pittsburg  Reduction  Company  have  begun  to 
use  the  electricity  in  reducing  aluminum  from 
the  mineral  known  as  bauxite,  an  oxide  of  the 
metal,  by  means  of  the  electric  furnace. 

Another  portion  of  the  power  is  to  be  used  to 
produce  carbide  of  calcium  for  the  manufacture 
of  acetylene  gas.  At  a  recent  electrical  exhibition 
held  in  New  York  city  a  model  of  the  Niagara 
plant  was  operated  by  an  electric  current  brought 
from  Niagara,  450  miles  distant ;  and  a  collection 
of  telephones  were  so  connected  that  the  spec- 
tator could  hear  the  roar  of  the  real  cataract. 

Thanks  to  the  foresight  of  New  York  State 
and  Canada,  the  scenery  of  the  Falls  has  been 
preserved  by  the  institution  of  public  parks,  and 
the  works  in  question  will' do  nothing  to  spoil  it, 
especially  as  they  will  be  free  from  smoke.  Mr. 
Bogarts,  State  Engineer  of  New  York,  estimates 
that  the  water  drawn  from  the  river  will  only 
lower  the  mean  depth  of  the  Falls  about  two 
inches,  and  will  therefore  make  no  appreciable 
difference  in  the  view.  Altogether,  the  enter- 
prise is  something  new  in  the  history  of  the 


MINOR  USES  OF  ELECTRICITY. 


143 


world.  It  is  not  only  the  grandest  application  of 
electrical  power,  but  one  of  the  most  remarkable 
feats  in  an  age  when  romance  has  become  science, 
and  science  has  become  romance. 


CHAPTER   IX. 

MINOR    USES    OF    ELECTRICITY. 

THE  electric  "  trembling  bell,"  now  in  common 
use,  was  first  invented  by  John  Mirand  in  1850. 
Figure  83  shows  the  scheme  of  the  circuit,  where 


G  P 

FIG.  83.— An  Electric  Trembling  Bell. 

B  is  a  small  battery,  say  two  or  three  "  dry  "  or 
Leclanche  cells,  joined  by  insulated  wire  to  P, 
a  press-button  or  contact  key,  and  G  an  electro- 
magnetic gong  or  bell.  On  pressing  the  button 
P,  a  spring  contact  is  made,  and  the  current 
flowing  through  the  circuit  strikes  the  bell.  The 
action  of  the  contact  key  will  be  understood 
from  figure  84,  where  P  is  the  press-button 
removed  to  show  the  underlying  mechanism, 
which  is  merely  a  metal  spring  A  over  a  metal 


144 


THE   STORY  OF   ELECTRICITY. 


plate  B.  The  spring  is  connected  by  wire  to  a 
pole  of  the  battery,  and  the  plate  to  a  terminal 
or  binding  screw  of  the  bell,  or  vice  versd.  When 


FIG.  84. 

the  button  P  is  pressed  by  the  finger  the  spring 
is  forced  against  .the  plate,  the  circuit  is  made, 
and  the  bell  rings.  On  releasing  the  button  it 
springs  back,  the  circuit  is  broken,  and  the  bell 
stops. 

Figure  85  shows  the  inner  mechanism  of  the 
bell,  which  consists  of  a  double-poled  electro- 
magnet AT,  having  a  soft  iron  armature  A  hinged 
on  a  straight  spring  or  tongue  6",  with  one  end 
fixed,  and  the  other  resting  against  a  screw  con- 
tact T.  The  hammer  H  projects  from  the  arma- 
ture beside  the  edge  of  the  gong  E. 

In  passing  through  the  instrument  the  current 
proceeds  from  one  terminal,  say  that  on  the  right, 
by  the  wire  Wto  the  screw  contact  T,  and  thence 
by  the  spring  £  through  the  bobbins  of  the  elec- 
tromagnet to  the  other  terminal.  The  electro- 
magnet attracts  the  armature  A,  and  the  hammer 
H  strikes  the  gong ;  but  in  the  act  the  spring  S 
is  drawn  from  the  contact  T,  and  the  circuit  is 
broken.  Consequently  the  electromagnet,  no 


MINOR   USES  OF   ELECTRICITY. 


145 


longer   excited,   lets   the   armature   go,   and   the 
spring  leaps  back  against  the  contact   T,  with- 


FIG.  85. 

drawing  the  hammer  from  the  gong.  But  the  in- 
strument is  now  as  it  was  at  first,  the  current  again 
flows,  and  the  hammer  strikes  the  gong,  only  to 
fly  back  a  second  time.  In  this  way,  as  long  as 
the  button  is  pressed  by  the  operator,  the  hammer 
will  continue  to  tap  the  bell  and  give  a  ringing 
sound.  Press-buttons  are  of  various  patterns,  and 
either  affixed  to  the  wall  or  inserted  in  the  handle 
of  an  ordinary  bell-pull,  as  shown  in  figure  86. 
10 


146 


THE  STORY  OF  ELECTRICITY. 


The  ordinary  electric  bell  actuated  by  a  bat- 
tery is  liable  to  get  out  of  order  owing  to  the 
battery  spending  its  force,  or  to  the 
contacts  becoming  dirty.  Magneto- 
electric  bells  have,  therefore,  been 
introduced  of  late  years.  With  these 
no  battery  or  interrupting  contacts 
are  required,  since  the  bell-pull  or 
press-button  is  made  in  the  form  of 
a  small  dynamo  which  generates  the 
current  when  it  is  pulled  or  pushed. 
Figure  87  illustrates  a  form  of  this 
apparatus,  where  M  P  is  the  bell- 
pull  and  B  the  bell,  these  being  con- 
nected by  a  double  wire  W,  to  con- 
vey the  current.  The  bell-pull  con- 
sists of  a  horseshoe  magnet  M,  hav- 
ing a  bobbin  of  insulated  wire  be- 
tween its  poles,  and  mounted  on  a 
spindle.  When  the  key  P  is  turned 
round  by  the  hand,  the  bobbin  moves 
in  the  magnetic  field  between  the 
poles  of  the  magnet,  and  the  current 
thus  generated  circulates  in  the  wires 
W,  and  passing  through  an  electro- 
magnet under  the  bell,  attracts  its  armature,  and 
strikes  the  hammer  on  the  bell.  Of  course  the 
bell  may  be  placed  at  any  distance  from  the  gen- 
erator. In  other  types  the  current  is  generated 
and  the  bell  rung  by  the  act  of  pulling,  as  in  a 
common  house-bell. 

Electric  bells  in  large  houses  and  hotels  are 
usually  fitted  up  with  indicators,  as  shown  in 
figure  88,  which  tell  the  room  from  which  the 
call  proceeds.  They  are  serviceable  as  instan- 
taneous signals,  annunciators,  and  alarms  in  many 


FIG.  86. 


MINOR   USES  OF   ELECTRICITY. 


147 


different  ways.     An  outbreak  of  fire  can  be  an- 
nounced by  causing  the  undue  rise  of  tempera- 


FIG.  87. 

ture  to  melt  a  piece  of  tallow  or  fusible  metal, 
and  thus  release  a  weight,  which  falls  on  a  press- 
button,  and  closes  the  circuit  of  an  electric  bell. 
Or,  the  rising  temperature  may  expand  the  mer- 
cury in  a  tube  like  that  of  a  thermometer  until  it 
connects  two  platinum  wires  fused  through  the 
glass  and  in  circuit  with  a  bell.  Some  employ  a 
curving  bi-metallic  spring  to  make  the  necessary 
contact.  The  spring  is  made  by  soldering  strips 
of  brass  and  iron  back  to  back,  and  as  these 
metals  expand  unequally  when  heated,  the  spring 
is  deformed,  and  touches  the  contact  which  is 
connected  in  the  circuit,  thus  permitting  the  cur- 


THE  STORY  OF   ELECTRICITY. 


»n.jie»  ttjtwra  mt  MMTI* 


rent  to  ring  the  bell.  A  still  better  device,  how- 
ever, is  a  small  box  containing  a  thin  metallic 

diaphragm,  which 
expands  with  the 
heat,  and  sagging 
in  the  centre,  touch- 
es a  contact  screw, 
thus  completing  the 
circuit,  and  allow- 
ing the  current  to 
pass. 

These  automatic 
or  self-acting  fire- 
alarms  can,  of 
course,  be  con- 
nected in  the  cir- 
cuit of  the  ordinary 
street  fire  -  alarms, 
which  are  usually 
worked  by  pulling 
a  handle  to  make 
the  necessary  con- 
tact. 

From  what  has 
been  said,  it  will  be 

easy  to  understand  how  the  stealthy  entrance  of 
burglars  into  a  house  can  be  announced  by  an 
electric  bell  or  warning  lamp.  If  press-buttons  or 
contact-keys  are  placed  on  the  sashes  of  the  win- 
dows, the  posts  of  the  door,  or  the  treads  of  the 
stair,  so  that  when  the  window  or  door  is  opened, 
or  the  tread  bends  under  the  footstep,  an  electric 
circuit  is  closed,  the  alarm  will  be  given.  Of 
course,  the  connections  need  only  be  arranged 
when  the  device  is  wanted.  Shops  and  offices 
can  be  guarded  by  making  the  current  show  a 


MINOR   USES  OF   ELECTRICITY.  149 

red  light  from  a  lamp  hung  in  front  of  the  prem- 
ises, so  that  the  night  watchman  can  see  it  on 
his  beat.  This  can  readily  be  done  by  adjusting 
an  electromagnet  to  drop  a  screen  of  red  glass 
before  the  flame  of  the  lamp.  Safes  and  show- 
cases forcibly  opened  can  be  made  to  signal  the 
fact,  and  recently  in  the  United  States  a  thief  was 
photographed  by  a  flashlight  kindled  in  this  way, 
and  afterwards  captured  through  the  likeness. 

The  level  of  water  in  cisterns  and  reservoirs 
can  be  told  in  a  similar  manner  by  causing  a 
float  to  rise  with  the  water  and  make  the  re- 
quired contact.  The  degree  of  frost  in  a  con- 
servatory can  also  be  announced  by  means  of 
the  mercury  "  thermostat,"  already  described, 
or  some  equivalent  device.  There  are,  indeed, 
many  actual  or  possible  applications  of  a  similar 
kind. 

The  Massey  log  is  an  instrument  for  telling 
the  speed  of  a  ship  by  the  revolutions  of  a  "  fly  " 
as  it  is  towed  through  the  water,  and  by  making 
the  fly  complete  a  circuit  as  it  revolves  the  num- 
ber of  turns  a  second  can  be  struck  by  a  bell  on 
board.  In  one  form  of  the  "  electric  log,"  the 
current  is  generated  by  the  chemical  action  of 
zinc  and  copper  plates  attached  to  the  log,  and 
immersed  in  the  sea  water,  and  in  others  pro- 
vided by  a  battery  on  the  ship. 

Captain  M'Evoy  has  invented  an  alarm  for 
torpedoes  and  torpedo  boats,  which  is  a  veritable 
watchdog  of  the  sea.  It  consists  of  an  iron  bell- 
jar  inverted  in  the  water,  and  moored  at  a  depth 
below  the  agitation  of  the  waves.  In  the  upper 
part  of  the  jar,  where  the  pressure  of  the  air 
keeps  back  the  water,  there  is  a  delicate  needle 
contact  in  circuit  with  a  battery  and  an  electric 


150  THE   STORY   OF   ELECTRICITY. 

bell  or  lamp,  as  the  case  may  be,  on  the  shore. 
Waves  of  sound  passing  through  the  water  from 
the  screw  propeller  of  the  torpedo,  or,  indeed,  any 
ship,  make  and  break  the  sensitive  contact,  and 
ring  the  bell  or  light  the  lamp.  The  apparatus 
is  intended  to  alarm  a  fleet  lying  at  anchor  or  a 
port  in  time  of  war. 

Electricity  has  also  been  employed  to  register 
the  movements  of  weathercocks  and  anemometers. 
A  few  years  ago  it  was  applied  successfully  to 
telegraph  the  course  marked  by  a  steering  com- 
pass to  the  navigating  officer  on  the  bridge. 
This  was  done  without  impeding  the  motion  of 
the  compass  card  by  causing  an  electric  spark  to 
jump  from  a  light  pointer  on  the  card  to  a  series 
of  metal  plates  round  the  bowl  of  the  compass, 
and  actuate  an  electric  alarm. 

The  "  Domestic  Telegraph,"  an  American  de- 
vice, is  a  little  dial  apparatus  by  which  a  citizen 
can  signal  for  a  policeman,  doctor,  messenger,  or 
carriage,  as  well  as  a  fire  engine,  by  the  simple  act 
of  setting  a  hand  on  the  dial. 

Alexander  Bain  was  the  first  to  drive  a  clock 
with  electricity  instead  of  weights,  by  employing 
a  pendulum  having  an  iron  bob.  which  was  at- 
tracted to  one  side  and  the  other  by  an  electro- 
magnet, but  as  its  rate  depends  on  the  constancy 
of  the  current,  which  is  not  easy  to  maintain,  the 
invention  has  not  come  into  general  use.  The 
"  butterfly  clock  "  of  Lemoine,  which  we  illustrate 
in  figure  89,  is  an  improved  type,  in  which  the  bob 
of  soft  iron  P  swings  to  and  fro  over  the  poles 
of  a  double  electro  magnet  M  in  circuit  with  a 
battery  and  contact  key.  When  the  rate  is  too 
slow  the  key  is  closed,  and  a  current  passing 
through  the  electromagnet  pulls  on  the  pendu- 


MINOR   USES   OF   ELECTRICITY. 


lum,  thus  correcting  the  clock.  This  is  done  by 
the  ingenious  device  of  Hipp,  shown  in  figure 
90,  where  M  is  the  electromagnet,  P  the  iron 
bob,  from  which  projects  a  wire  bearing  a  light 
vane  B  of  mica  in  the  shape 
of  a  butterfly.  As  the  bob 
swings  the  wire  drags  over 
the  hump  of  the  metal  spring 
S,  and  when  the  bob  is  going 
too  slowly  the  wire  thrusts 
the  spring  into  contact  with 
another  spring  T  below,  thus 
closing  the  circuit,  and  send- 
ing a  current  through  the 
magnet  M,  which  attracts  the 
bob  and  gives  a  fillip  to  the 
pendulum. 

Local  clocks  controlled 
from  a  standard  clock  by  elec- 
tricity have  been  more  suc- 
cessful in  practice,  and  are 
employed  in  several  towns — 
for  example,  Glasgow.  Be- 
hind local  dials  are  electro- 
magnets which,  by  means  of 
an  armature  working  a  frame  and  ratchet  wheel, 
move  the  hands  forward  every  minute  or  half- 
minute  as  the  current  is  sent  from  the  standard 
clock. 

The  electrical  chronograph  is  an  instrument 
for  measuring  minute  intervals  of  time  by  means 
of  a  stylus  tracing  a  line  on  a  band  of  travelling 
paper  or  a  revolving  barrel  of  smoked  glass.  The 
current,  by  exciting  an  electromagnet,  jerks  the 
stylus,  and  the  interval  between  two  jerks  is 
found  from  the  length  of  the  trace  between  them 


FIG.  89.— The  Electric 
"Butterfly"  Clock. 


152 


THE   STORY   OF   ELECTRICITY. 


and  the  speed  of  the  paper  or  smoked  surface. 
Retarded  clocks  are  sometimes  employed  as 
electric  meters  for  registering  the  consumption 
of  electricity.  In  these  the  current  to  be  mea- 
sured flows  through  a  coil  beneath  the  bob  of  the 
pendulum,  which  is  a  magnet,  and  thus  affects  the 


FIG.  90. 

rate.  In  other  meters  the  current  passes  through 
a  species  of  galvanometer  called  an  ampere  meter, 
and  controls  a  clockwork  counter.  In  a  third 
kind  of  meter  the  chemical  effect  of  the  current 
is  brought  into  play — that  of  Edison,  for  example, 
decomposing  sulphate  of  copper,  or  more  com- 
monly of  zinc. 

The  electric  light  is  now  used  for  signalling 
and  advertising  by  night  in  a  variety  of  ways. 
Incandescent  lamps  inside  a  translucent  balloon, 
and  their  light  controlled  by  a  current  key,  as  in 


MINOR   USES  OF   ELECTRICITY.  153 

a  telegraph  circuit,  so  as  to  give  long  and  short 
flashes,  according  to  the  Morse  code,  are  em- 
ployed in  the  army.  Signals  at  sea  are  also 
made  by  a  set  of  red  and  white  glow-lamps, 
which  are  combined  according  to  the  code  in  use. 
The  powerful  arc  lamp  is  extremely  useful  as  a 
"  search  light,"  especially  on  men-of-war  and 
fortifications,  and  it  has  also  been  tried  in  sig- 
nalling by  projecting  the  beam  on  the  clouds  by 
way  of  a  screen,  and  eclipsing  it  according  to  a 
given  code. 

In  1879^  Professor  Graham  Bell,  the  inventor 
of  the  speaking  telephone,  and  Mr.  Summer 
Tainter,  brought  out  an  ingenious  apparatus 
called  the  photophone,  by  which  music  and 
speech  were  sent  along  a  beam  of  light  for 
several  hundred  yards.  The  action  of  the  photo- 
phone  is  based  on  the  peculiar  fact  observed  in 
1873  by  Mr.  J.  E.  Mayhew,  that  the  electrical  re- 
sistance of  crystalline  selenium  diminishes  when 
a  ray  of  light  falls  upon  it.  Figure  91  shows 


r 

FIG.  91.— The  Photophone. 

how  Bell  and  Tainter  utilised  this  property  in  the 
telephone.  A  beam  of  sun  or  electric  light,  con- 
centrated by  a  lens  Z,  is  reflected  by  a  thin  mirror 
My  and  after  traversing  another  lens  Z,  travels 
to  the  parabolic  reflector  R,  in  the  focus  of 


154  THE  STORY  OF  ELECTRICITY. 

which  there  is  a  selenium  .resistance  in  circuit 
with  a  battery  B  and  two  telephones  T  T'.  Now, 
when  a  person  speaks  into  the  tube  at  the  back 
of  the  mirror  J/,  the  light  is  caused  to  vibrate 
with  the  sounds,  and  a  wavering  beam  falls  on  the 
selenium,  changing  its  resistance  to  the  cur- 
rent. The  strength  of  the  current  is  thus  varied 
with  the  sonorous  waves,  and  the  words  spoken 
by  the  transmitter  are  heard  in  the  telephones 
by  the  receiver.  The  photophone  is,  however, 
more  of  a  scientific  toy  than  a  practical  instru- 
ment. 

Becquerel,  the  French  chemist,  found  that 
two  plates  of  silver  freshly  coated  with  silver 
from  a  solution  of  chloride  of  silver  and  plunged 
into  water,  form  a  voltaic  cell  which  is  sensitive 
to  light.  This  can  be  seen  by  connecting  the 
plates  through  a  galvanometer,  and  allowing  a 
ray  of  light  to  fall  upon  them.  Other  combina- 
tions of  the  kind  have  been  discovered,  and 
Professor  Minchin,  the  Irish  physicist,  has  used 
one  of  these  cells  to  measure  the  intensity  of 
starlight. 

The  "  induction  balance  "  of  Professor  Hughes 
is  founded  on  the  well-known  fact  that  a  current 
passing  in  one  wire  can  induce  a  sympathetic 
current  in  a  neighbouring  wire.  The  arrange- 
ment will  be  understood  from  figure  92,  where  P 
and  PI  are  two  similar  coils  or  bobbins  of  thick 
wire  in  circuit  with  a  battery  B  and  a  micro- 
phone M,  while  S  and  Si  are  two  similar  coils  or 
bobbins  of  fine  wire  in  circuit  with  a  telephone 
T.  It  need  hardly  be  said  that  when  the  micro- 
phone M  is  disturbed  by  a  sound,  the  current  in 
the  primary  coils  P  P^  will  induce  a  correspond- 
ing current  in  the  secondary  coils  S  S\\  but  the 


MINOR   USES   OF  ELECTRICITY.  155 

coils  6"  Sl  are  so  wound  that  the  induction  of  P 
on  S  neutralises  the  induction  of  P±  on  Sl9  and 
no  current  passes  in  the  secondary  circuit,  hence 
no  sound  is  heard  in  the  telephone.  When,  how- 


B      M 

FIG.  92.— The  Induction  Balance. 

ever,  this  balance  of  induction  is  upset  by  bring- 
ing a  piece  of  metal — say,  a  coin — near  one  or 
other  of  the  coils  5  Sl9  a  sound  will  be  heard  in 
the  telephone. 

The  induction  balance  has  been  used  as  a 
"  Sonometer  "  for  measuring  the  sense  of  hear- 
ing, and  also  for  telling  base  coins.  The  writer 
devised  a  form  of  it  for  "  divining  "  the  presence 
of  gold  and  metallic  ores  which  has  been  applied 
by  Captain  M'Evoy  in  his  "  submarine  detector  " 
for  exploring  the  sea  bottom  for  lost  anchors  and 
sunken  treasure.  When  President  Garfield  was 
shot,  the  position  of  the  bullet  was  ascertained 
by  a  similar  arrangement. 

The  microphone  as  a  means  of  magnifying 
feeble  sounds  has  been  employed  for  localising 
the  leaks  in  water  pipes  and  in  medical  examina- 
tions. Some  years  ago  it  saved  a  Russian  lady 
from  premature  burial  by  rendering  the  faint  beat- 
ing of  her  heart  audible. 


156  THE  STORY  OF   ELECTRICITY. 

Edison's  electric  pen  is  useful  in  copying  let- 
ters. It  works  by  puncturing  a  row  of  minute 
holes  along  the  lines  of  the  writing,  and  thus  pro- 
ducing a  stencil  plate,  which,  when  placed  over  a 
clean  sheet  of  paper  and  brushed  with  ink,  gives 
a  duplicate  of  the  writing  by  the  ink  penetrating 
the  holes  to  the  paper  below.  It  is  illustrated  in 
figure  93,  where  P  is  the  pen,  consisting  of  a  hol- 


FIG.  93.— The  Electric  Pen. 

low  stem  in  which  a  fine  needle  actuated  by  the 
armature  of  a  small  electromagnet  plies  rapidly 
up  and  down  and  pierces  the  paper.  The  current 
is  derived  from  a  small  battery  £,  and  an  inking 
roller  like  that  used  in  printing  serves  to  apply 
the  ink. 

In  1878  Mr.  Edison  announced  his  invention 
of  a  machine  for  the  storage  and  reproduction  of 
speech,  and  the  announcement  was  received  with 
a  good  deal  of  incredulity,  notwithstanding  the 
partial  success  of  Faber  and  others  in  devising 
mechanical  articulators.  The  simplicity  of  Edison's 
invention  when  it  was  seen  and  heard  elicited  much 
admiration,  and  although  his  first  instrument  was 
obviously  imperfect,  it  was  nevertheless  regarded 
as  the  germ  of  something  better.  If  the  words 
spoken  into  the  instrument  were  heard  in  the  first 


MINOR   USES  OF  ELECTRICITY.  157 

place,  the  likeness  of  the  reproduction  was  found 
to  be  unmistakable.  Indeed,  so  faithful  was  the 
replica,  that  a  member  of  the  Academy  of  Sci- 
ences, Paris,  stoutly  maintained  that  it  was  due  to 
ventriloquism  or  some  other  trickery.  It  was  evi- 
dent, however,  that  before  the  phonograph  could 
become  a  practical  instrument,  further  improve- 
ments in  the  nicety  of  its  articulation  were  re- 
quired. The  introduction  of  the  electric  light  di- 
verted Mr.  Edison  from  the  task  of  improving  it, 
although  he  does  not  seem  to  have  lost  faith  in 
his  pet  invention.  During  the  next  ten  years  he 
accumulated  a  large  fortune,  and  was  the  princi- 
pal means  of  introducing  both  electric  light  and 
power  to  the  world  at  large.  This  done,  how- 
ever, he  returned  to  his  earlier  love,  and  has  at 
length  succeeded  in  perfecting  it  so  as  to  redeem 
his  past  promises  and  fulfil  his  hopes  regard- 
ing it. 

The  old  instrument  consisted,  as  is  well  known, 
of  a  vibrating  tympan  or  drum,  from  the  centre 
of  which  projected  a  steel  point  or  stylus,  in  such 
a  manner  that  on  speaking  to  the  tympan  its 
vibrations  would  urge  the  stylus  to  dig  into  a 
sheet  of  tinfoil  moving  past  its  point.  The  foil 
was  supported  on  a  grooved  barrel,  so  that  the 
hollow  of  the  groove  behind  it  permitted  the  foil 
to  give  under  the  point  of  the  stylus,  and  take  a 
corrugated  or  wavy  surface  corresponding  to  the 
vibrations  of  the  speech.  Thus  recorded  on  a 
yielding  but  somewhat  stiff  material,  these  undu- 
lations could  be  preserved,  and  at  a  future  time 
made  to  deflect  the  point  of  a  similar  stylus,  and 
set  a  corresponding  diaphragm  or  tympan  into  vi- 
bration, so  as  to  give  out  the  original  sounds,  or 
an  imitation  of  them. 


158  THE   STORY   OF   ELECTRICITY. 

Tinfoil,  however,  is  not  a  very  satisfactory 
material  on  which  to  receive  the  vibrations  in  the 
first  place.  It  does  not  precisely  respond  to  the 
movements  of  the  marking  stylus  in  taking  the 
impression,  and  does  not  guide  the  receiving  sty- 
lus sufficiently  well  in  reproducing  sounds.  Mr. 
Edison  has  therefore  adopted  wax  in  preference 
to  it ;  and  instead  of  tinfoil  spread  on  a  grooved 
support,  he  now  employs  a  cylinder  of  wax  to 
take  the  print  of  the  vibrations.  Moreover,  he 
no  longer  uses  the  same  kind  of  diaphragm  to 
print  and  receive  the  sounds,  but  employs  a  more 
delicate  one  for  receiving  them.  The  marking 
cylinder  is  now  kept  in  motion  by  an  electric 
motor,  instead  of  by  hand-turning,  as  in  the  earlier 
instrument. 

The  new  phonograph,  which  we  illustrate  in 
figure  94,  is  about  the  size  of  an  ordinary  sewing 
machine,  and  is  of  exquisite  workmanship,  the 
performance  depending  to  a  great  extent  on  the 
perfection  and  fitness  of  the  mechanism.  It  con- 
sists of  a  horizontal  spindle  *S,  carrying  at  one 
end  the  wax  cylinder  C,  on  which  the  sonorous 
vibrations  are  to  be  imprinted.  Over  the  cylin- 
der is  supported  a  diaphragm  or  tympan  7",  pro- 
vided with  a  conical  mouthpiece  M  for  speaking 
into.  Under  the  tympan  there  is  a  delicate  needle 
or  stylus,  with  its  point  projecting  from  the  centre 
of  the  tympan  downwards  to  the  surface  of  the 
wax  cylinder,  so  that  when  a  person  speaks  into 
the  mouthpiece,  the  voice  vibrates  the  tympan 
and  drives  the  point  of  the  stylus  down  into  the 
wax,  making  an  imprint  more  or  less  deep  in  ac- 
cordance with  the  vibrations  of  the  voice.  The 
cylinder  is  kept  revolving  in  a  spiral  path,  at  a 
uniform  speed,  by  means  of  an  electric  motor  E, 


MINOR   USES   OF  ELECTRICITY.  159 

fitted  with  a  sensitive  regulator  and  situated  at 
the  base  of  the  machine.    The  result  is  that  a  deli- 


FIG.  94.—  The  Phonograph. 

cate  and  ridgy  trace  is  cut  in  the  surface  of  wax 
along  a  spiral  line.  This  is  the  sound  record,  and 
by  substituting  a  finer  tympan  for  the  one  used  in 
producing  it,  the  ridges  and  inequalities  of  the  trace 
can  be  made  to  agitate  a  light  stylus  resting  on 
them,  and  cause  it  to  set  the  delicate  tympan  into 
vibrations  corresponding  very  accurately  to  those 
of  the  original  sounds.  The  tympan  employed 
for  receiving  is  made  of  gold-beater's  skin,  having 
a  stud  at  its  centre  and  a  springy  stylus  of  steel 
wire.  The  sounds  emitted  by  this  device  are 
almost  a  whisper  as  compared  to  the  original  ones, 
but  they  are  faithful  in  articulation,  which  is  the 
main  object,  and  they  are  conveyed  to  the  ear  by 
means  of  flexible  hearing-tubes. 

These   tympans  are  interchangeable   at  will, 


i6o 


THE  STORY  OF  ELECTRICITY. 


and  the  arm  which  carries  them  is  also  provided 
with  a  turning  tool  for  smoothing  the  wax  cylin- 
der prior  to  its  receiving  the  print.  The  cylinders 
are  made  of  different  sizes,  from  i  to  8  inches 
long  and  4  inches  in  diameter.  The  former  has  a 
storage  capacity  of  200  words.  The  next  in  size 
has  twice  that,  or  400  words,  and  so  on.  Mr. 
Edison  states  that  four  of  the  large  8-inch  cylin- 
ders can  record  all  "  Nicholas  Nickleby,"  which 
could  therefore  be  automatically  read  to  a  private 
invalid  or  to  a  number  of  patients  in  a  hospi- 
tal simultaneously,  by 
means  of  a  bunch  of 
hearing  -  tubes.  The 
cylinders  can  be  read- 
ily posted  like  letters, 
and  made  to  deliver 
their  contents  viva  voce  in  a  du- 
plicate phonograph,  every  tone 
and  expression  of  the  writer  be- 
ing rendered  with  more  or  less 
fidelity.  The  phonograph  has 
proved  serviceable  in  recording 
the  languages  and  dialects  of  van- 
ishing races,  as  well  as  in  teaching 
pronunciation. 

The  dimensions,  form,  and  con- 
sequent appearance  of  the  present 
commercial  American  phonograph 
are  quite  different  from  that  above 
described,  but  the  underlying  principles  and  op- 
erations are  identical. 

A  device  for  lighting  gas  by  the  electric  spark 
is  shown  in  figure  95,  where  A  is  a  flat  vulcanite 
box,  containing  the  apparatus  which  generates 
the  electricity,  and  a  stem  or  pointer  J3,  which 


FiG.  95. — An 
Electric  Gas 
Lighter. 


MINOR  USES  OF  ELECTRICITY.  l6l 

applies  the  spark  to  the  gas  jet.  The  generator 
consists  of  a  small  "  influence  "  machine,  which  is 
started  by  pressing  the  thumb-key  C  on  the  side 
of  the  box.  The  rotation  of  a  disc  inside  the  box 
produces  a  supply  of  static  electricity,  which 
passes  in  a  stream  of  sparks  between  two  contact- 
points  in  the  open  end  of  the  stem  D.  The  latter 
is  tubular,  and  contains  a  wire  insulated  from  the 
metal  of  the  tube,  and  forming  with  the  tube  the 
circuit  for  the  electric  discharge.  The  handle 
enables  the  contrivance  to  be  readily  applied. 
The  apparatus  is  one  of  the  few  successful  prac- 
tical applications  of  static  electricity. 

Other  electric  gas-lighters  consist  of  metal 
points  placed  on  the  burner,  so  that  the  electric 
spark  from  a  small  induction  coil  or  dynamo 
kindles  the  jet. 

A  platinum  wire  made  white-hot  by  the  pas- 
sage of  a  current  is  sometimes  used  to  light 
lamps,  as  shown  in  figure  96,  where  W  is  a  small 
spiral  of  platinum  connected  in  circuit  with  a 
generator  by  the  terminals  T  T.  When  the  lamp 
L  is  pressed  against  the  button  B  the  wire  glows 
and  lights  it. 

Explosives,  such  as  gunpowder  and  guncotton, 
are  also  ignited  by  the  electric  spark  from  an  in- 
duction coil  or  the  incandescence  of  a  wire.  Fig- 
ure 97  shows  the  interior  of  an  ordinary  electric 
fuse  for  blasting  or  exploding  underground  mines. 
It  consists  of  a  box  of  wood  or  metal  primed 
with  gunpowder  or  other  explosive,  and  a  plat- 
inum wire  P  soldered  to  a  pair  of  stout  copper 
wires  W,  insulated  with  guttapercha.  When  the 
current  is  sent  along  these  wires,  the  platinum 
glows  and  ignites  the  explosive.  Detonating 
fuses  are  primed  with  fulminate  of  mercury. 
ii 


162 


THE  STORY  OF   ELECTRICITY. 


Springs  for  watches  and  other  purposes  are 
tempered  by  heating  them  with  the  current  and 
quenching  them  in  a  bath  of  oil. 


FIG.  96.— An  Electric  Lamp  Lighter. 

Electrical  cautery  is  performed  with  an  in- 
candescent platinum  wire  in  lieu  of  the  knife, 
especially  for  such  operations  as  the  removal  of 
the  tongue  or  a  tumour. 

It  was  known  to  the  ancients  that  a  fish  called 
a  torpedo  existed  in  the  Mediterranean  which 
was  capable  of  administering  a  shock  to  persons 
and  benumbing  them.  The  torpedo,  or  "  electric 
ray,"  is  found  in  the  Atlantic  as  well  as  the  Med- 
iterranean, and  is  allied  to  the  skate.  It  has  an 
electric  organ  composed  of  800  or  1000  polygonal 


MINOR  USES  OF  ELECTRICITY.  163 

cells  in  its   head,  and  the  discharge,  which  ap- 
pears to  be  a  vibratory  current,  passes  from  the 


FIG.  97. — An  Electric  Fuse. 

back  or  positive  pole  to  the  belly  or  negative  pole 
through  the  water.  The  gymotus,  or  Surinam  eel, 
which  attains  a  length  of  five  or  six  feet,  has  an 
electric  organ  from  head  to  tail,  and  can  give  a 
shock  sufficient  to  kill  a  man.  Humboldt  has 
left  a  vivid  picture  of  the  frantic  struggles  of  wild 
horses  driven  by  the  Indians  of  Venezuela  into  the 
ponds  of  the  savannahs  infested  by  these  eels,  in 
order  to  make  them  discharge  their  thunderbolts 
and  be  readily  caught. 

Other  fishes — the  silurus,  malapterurus,  and  so 
on — are  likewise  endowed  with  electric  batteries 
for  stunning  and  capturing  their  prey.  The  ac- 
tion of  the  organs  is  still  a  mystery,  as,  indeed,  is 
the  whole  subject  of  animal  electricity.  Nobili 
and  Matteucci  discovered  that  feeble  currents 
are  generated  by  the  excitation  of  the  nerves  and 
the  contraction  of  the  muscles  in  the  human  sub- 
ject. 

Electricity  promises  to  become  a  valuable 
remedy,  and  currents — continuous,  intermittent, 
or  alternating — are  applied  to  the  body  in  nerv- 
ous and  muscular  affections  with  good  effect; 
but  this  should  only  be  done  under  medical  ad- 
vice, and  with  proper  apparatus. 

In  many  cases  of  severe  electric  shock  or 
lightning  stroke,  death  is  merely  apparent,  and 


164 


THE   STORY   OF   ELECTRICITY. 


the  person  may  be  brought  back  to  life  by  the 
method  of  artificial  respiration  and  rhythmic  trac- 
tion of  the  tongue,  as  applied  to  the  victims  of 
drowning  or  dead  faint. 

A  good  lightning  conductor  should  not  have 
a  higher  electrical  resistance  than  10  ohms  from 
the  point  to  the  ground,  including  the  "  earth " 
contact.  Exceptionally  good  conductors  have 
only  about  5  ohms.  A  high  resistance  in  the  rod 
is  due  either  to  a  flaw  in  the  conductor  or  a  bad 
earth  connection,  and  in  such  a  case  the  rod  may 
be  a  source  of  danger  instead  of  security,  since 
the  discharge  is  apt  to  find  its  way  through  some 
part  of  the  building  to  the  ground,  rather  than 
entirely  by  the  rod.  It  is,  therefore,  important  to 
test  lightning  conductors  from  time  to  time,  and 
the  magneto-electric  tester  of  Siemens,  which  we 
illustrate  in  figures  98  and  99,  is  very  serviceable 


FIG.  98. 


for  the  purpose,  and  requires  no  battery.  The 
apparatus  consists  of  a  magneto-electric  machine 
M,  which  generates  the  testing  current  by  turn- 
ing a  handle,  and  a  Wheatstone  bridge.  The 


MINOR   USES  OF  ELECTRICITY.  165 

latter  comprises  a  ring  of  German  silver  wire, 
forming  two  branches.  A  contact  lever  P  moves 
over  the  ring,  and  is  used  as  a  battery  key.  A 
small  galvanometer  G  shows  the  indications  of 


FIG.  99. 

the  testing  current.  A  brass  sliding  piece  6*  puts 
the  galvanometer  needle  in  and  out  of  action. 
There  are  also  several  connecting  terminals,  b  £', 
/,  &c.,  and  a  comparison  resistance  R  (figure  98). 
A  small  key  K  is  fixed  to  the  terminal  /  (figure 
99),  and  used  to  put  the  current  on  the  lightning- 
rod,  or  take  it  off  at  will.  A  leather  bag  A  at 
one  side  of  the  wooden  case  (figure  99)  holds  a 
double  conductor  leading  wire,  which  is  used  for 
connecting  the  magneto-electric  machine  to  the 
bridge.  On  turning  the  handle  of  M  the  current 
is  generated,  and  on  closing  the  key  K  it  circu- 
lates from  the  terminals  of  the  machine  through 
the  bridge  and  the  lightning-rod  joined  with  the 
latter.  The  needle  of  the  galvanometer  is  de- 
flected by  it,  until  the  resistance  in  the  box  R  is 
adjusted  to  balance  that  in  the  rod.  When  this 


1 66  THE  STORY  OF  ELECTRICITY. 

is  so,  the  galvanometer  needle  remains  at  rest. 
In  this  way  the  resistance  of  the  rod  is  told,  and 
any  change  in  it  noted.  In  order  to  effect  the 
test,  it  is  necessary  to  have  two  earth  plates,  JS1 
and  £2,  one  (£l)  that  of  the  rod,  and  the  other 
(E2)  that  for  connecting  to  the  testing  apparatus 
by  the  terminal  bl  (figure  99).  The  whole  instru- 
ment only  weighs  about  9  Ibs.  In  order  to  test 
the  "  earth  "  alone,  a  copper  wire  should  be  sol- 
dered to  the  rod  at  a  convenient  height  above  the 
ground,  and  terminal  screws  fitted  to  it,  as  shown 
at  T  (figure  99),  so  that  instead  of  joining  the 
whole  rod  in  circuit  with  the  apparatus,  only  that 
part  from  T  downwards  is  connected.  The  Hon. 
R.  Abercrombie  has  recently  drawn  attention  to 
the  fact  that  there  are  three  types  of  thunder- 
storm in  Great  Britain.  The  first,  or  squall 
thunderstorms,  are  squalls  associated  with  thun- 
der and  lightning.  They  form  on  the  sides  of 
primary  cyclones.  The  second,  or  commonest 
thunderstorms,  are  associated  with  secondary  cy- 
clones, and  are  rarely  accompanied  by  squalls. 
The  third,  or  line  thunderstorms,  take  the  form 
of  narrow  bands  of  rain  and  thunder — for  ex- 
ample, 100  miles  long  by  5  to  10  miles  broad. 
They  cross  the  country  rapidly,  and  nearly  broad- 
side on.  These  are  usually  preceded  by  a  violent 
squall,  like  that  which  capsized  the  Eurydice. 

The  gloom  of  January,  1896,  with  its  war  and 
rumours  of  war,  was,  at  all  events,  relieved  by  a 
single  bright  spot.  Electricity  has  surprised  the 
world  with  a  new  marvel,  which  confirms  her 
title  to  be  regarded  as  the  most  miraculous  of  all 
the  sciences.  Within  the  past  twenty  years  she 
has  given  us  the  telephone  of  Bell,  enabling  Lon- 
don to  speak  with  Paris,  and  Chicago  with  New 


MINOR  USES  OF  ELECTRICITY. 

York ;  the  microphone  of  Hughes,  which  makes 
the  tread  of  a  fly  sound  like  the  "tramp  of  an 
elephant,"  as  Lord  Kelvin  has  said ;  the  phono- 
graph of  Edison,  in  which  we  can  hear  again  the 
voices  of  the  dead  ;  the  electric  light  which  glows 
without  air  and  under  water,  electric  heat  without 
fire,  electric  power  without  fuel,  and  a  great  deal 
more  beside.  To  these  triumphs  we  must  now 
add  a  means  of  photographing  unseen  objects, 
such  as  the  bony  skeletons  in  the  living  body, 
and  so  revealing  the  invisible. 

Whether  it  be  that  the  press  and  general  pub- 
lic are  growing  more  enlightened  in  matters  of 
science,  or  that  Professor  Rontgen's  discovery 
appeals  in  a  peculiar  way  to  the  popular  imagina- 
tion, it  has  certainly  evoked  a  livelier  and  more 
sudden  interest  than  either  the  telephone,  micro- 
phone, or  phonograph.  I  was  present  when  Lord 
Kelvin  first  announced  the  invention  of  the  tele- 
phone to  a  British  audience,  and  showed  the  in- 
strument itself,  but  the  intelligence  was  received 
so  apathetically  that  I  suspect  its  importance  was 
hardly  realised.  It  fell  to  my  own  lot,  a  few 
years  afterwards,  to  publish  the  first  account  of 
the  phonograph  in  this  country,  and  I  remember 
that,  between  incredulity  on  the  one  hand,  and 
perhaps  lack  of  scientific  interest  on  the  other,  a 
considerable  time  elapsed  before  the  public  at 
large  were  really  impressed  by  the  invention. 
Perhaps  the  uncanny  and  mysterious  results  of 
Rontgen's  discovery,  which  seem  to  link  it  with 
the  "  black  arts,"  have  something  to  do  with 
the  quickness  of  its  reception  by  all  manner  of 
people. 

Like  most,  if  not  all,  discoveries  and  inven- 
tions, it  is  the  outcome  of  work  already  done  by 


1 68  THE  STORY  OF  ELECTRICITY. 

other  men.  In  the  early  days  of  electricity  it 
was  found  that  when  an  electric  spark  from  a 
frictional  machine  was  sent  through  a  glass  bulb 
from  which  the  air  had  been  sucked  by  an  air 
pump,  a  cloudy  light  filled  the  bulb,  which  was 
therefore  called  an  "  electric  egg."  Hittorf  and 
others  improved  on  this  effect  by  employing  the 
spark  from  an  induction  coil  and  large  tubes, 
highly  exhausted  of  air,  or  containing  a  rare  in- 
fusion of  other  gases,  such  as  hydrogen.  By  this 
means  beautiful  glows  of  various  colours,  resem- 
bling the  tender  hues  of  the  tropical  sky,  or  the 
fleeting  tints  of  the  aurora  borealis,  were  pro- 
duced, and  have  become  familiar  to  us  in  the 
well-known  Geissler  tubes. 

Crookes,  the  celebrated  English  chemist,  went 
still  further,  and  by  exhausting  the  bulbs  with 
an  improved  Sprengel  air-pump,  obtained  an 
extremely  high  vacuum,  which  gave  remarkable 
effects  (page  120).  The  diffused  glow  or  cloudy 
light  of  the  tube  now  shrank  into  a  single  stream, 
which  joined  the  sparking  points  inserted  through 
the  ends  of  the  tube  as  with  a  luminous  thread. 
A  magnet  held  near  the  tube  bent  the  streamer 
from  its  course;  and  there  was  a  dark  space  or 
gap  in  it  near  the  negative  point  or  cathode,  from 
which  proceeded  invisible  rays,  having  the  prop- 
erty of  impressing  a  photographic  plate,  and  of 
rendering  matter  in  general  on  which  they  im- 
pinged phosphorescent,  and,  in  course  of  time, 
red-hot.  Where  they  strike  on  the  glass  of  the 
tube  it  is  seen  to  glow  with  a  green  or  bluish 
phosphorescence,  and  it  will  ultimately  soften 
with  heat. 

These  are  the  famous  "  cathode  rays  "  of  which 
we  have  recently  heard  so  much,  Apparently 


MINOR   USES  OF   ELECTRICITY.  169 

they  cannot  be  produced  except  in  a  very  high 
vacuum,  where  the  pressure  of  the  air  is  about 
i-iopth  millionth  of  an  atmosphere,  or  that  which 
it  is  some  90  or  100  miles  above  the  earth.  Mr. 
Crookes  regards  them  as  a  stream  of  airy  particles 
electrified  by  contact  with  the  cathode  or  nega- 
tive discharging  point,  and  repelled  from  it  in 
straight  lines.  The  rarity  of  the  air  in  the  tube 
enables  these  particles  to  keep  their  line  without 
being  jostled  by  the  other  particles  of  air  in 
the  tube.  A  molecular  bombardment  from  the 
cathode  is,  in  his  opinion,  going  on,  and  when 
the  shots,  that  is  to  say,  the  molecules  of  air, 
strike  the  wall  of  the  tube,  or  any  other  body 
within  the  tube,  the  shock  gives  rise  to  phos- 
phorescence or  fluorescence  and  to  heat.  This, 
in  brief,  is  the  celebrated  hypothesis  of  "  radiant 
matter,"  which  has  been  supported  in  the  United 
Kingdom  by  champions  such  as  Lord  Kelvin,  Sir 
Gabriel  Stokes,  and  Professor  Fitzgerald,  but 
questioned  abroad  by  Goldstein,  Jaumann,  Wiede- 
mann,  Ebert,  and  others. 

Lenard,  a  young  Hungarian,  pupil  of  the  illus- 
trious Heinrich  Hertz,  was  the  first  to  inflict  a 
serious  blow  on  the  hypothesis,  by  showing  that 
the  cathode  rays  could  exist  outside  the  tube  in 
air  at  ordinary  pressure.  Hertz  had  found  that  a 
thin  foil  of  aluminium  was  penetrated  by  the  rays, 
and  Lenard  made  a  tube  having  a  "  window  "  of 
aluminium,  through  which  the  rays  darted  into 
the  open  air.  Their  path  could  be  traced  by  the 
bluish  phosphorescence  which  they  excited  in  the 
air,  and  he  succeeded  in  getting  them  to  pene- 
trate a  thin  metal  box  and  take  a  photograph  in- 
side it.  But  if  the  rays  are  a  stream  of  radiant 
matter  which  can  only  exist  in  a  high  vacuum, 


1 70  THE  STORY  OF  ELECTRICITY. 

how  can  they  survive  in  air  at  ordinary  pressure  ? 
Lenard's  experiments  certainly  favour  the  hy- 
pothesis of  their  being  waves  in  the  luminiferous 
ether. 

Professor  Rontgen,  of  Wiirzburg,  profiting  by 
Lenard's  results,  accidentally  discovered  that  the 
rays  coming  from  a  Crookes  tube,  through  the 
glass  itself,  could  photograph  the  bones  in  the 
living  hand,  coins  inside  a  purse,  and  other  ob- 
jects covered  up  or  hid  in  the  dark.  Some  bodies, 
such  as  flesh,  paper,  wood,  ebonite,  or  vulcanised 
fibre,  thin  sheets  of  metal,  and  so  on,  are  more  or 
less  transparent,  and  others,  such  as  bones,  car- 
bon, quartz,  thick  plates  of  metal,  are  more  or 
less  opaque  to  the  rays.  The  human  hand,  for 
example,  consisting  of  flesh  and  bones,  allows 
the  rays  to  pass  easily  through  the  flesh,  but  not 
through  the  bones.  Consequently,  when  it  is  in- 
terposed between  the  rays  and  a  photographic 
plate,  the  skeleton  inside  is  photographed  on  the 
plate.  A  lead  pencil  photographed  in  this  way 
shows  only  the  black  lead,  and  a  razor  with  a 
horn  handle  only  the  blade. 

Thanks  to  the  courtesy  of  Mr.  A.  A.  Camp- 
bell Swinton,  of  the  firm  of  Swinton  &  Stanton, 
the  well-known  electrical  engineers,  of  Victoria 
Street,  Westminster,  a  skilful  experimentalist, 
who  was  the  first  to  turn  to  the  subject  in  Eng- 
land, I  have  witnessed  the  taking  of  these 
"  shadow  photographs,"  as  they  are  called,  some- 
what erroneously,  for  "  radiographs"  or  "crypto- 
graphs "  would  be  a  better  word,  and  shall  briefly 
describe  his  method.  Rontgen  employs  an  induc- 
tion coil  insulated  in  oil  to  excite  the  Crookes 
tube  and  yield  the  rays,  but  Mr.  Swinton  uses  a 
"  high  frequency  current,"  obtained  from  appara- 


MINOR  USES  OF   ELECTRICITY. 


FIG.  100. —Photographing  the  Unseen. 


172 


THE  STORY  OF  ELECTRICITY. 


tus  similar  to  that  of  Tesla,  and  shown  in  figure 
100,  namely,  a  high  frequency  induction  coil  in- 
sulated by  means  of  oil  and  excited  by  the  con- 
tinuous discharge  of  twelve  half-gallon  Leyden 
jars  charged  by  an  alternating  current  at  a  pres- 
sure of  20,000  volts  produced  by  an  ordinary 
large  induction  coil  sparking  across  its  high  pres- 
sure terminals. 

A  vacuum  bulb  connected  between  the  dis- 
charge terminals  of  the  high  frequency  coil,  as 


^ 

—      .  .->-  .•»«•«>-  ._  «.  ^ 

FIG.  ioi.  —  Photographing  the  Skeleton. 


shown  in  figure  ioi,  was  illuminated  with  a  pink 
glow,  which  streamed  from  the  negative  to  the 
positive  pole  —  that  is  to  say,  the  cathode  to  the 
anode,  and  the  glass  became  luminous  with  bluish 
phosphorescence  and  greenish  fluorescence.  Im- 
mediately under  the  bulb  was  placed  my  naked 
hand  resting  on  a  photographic  slide  containing 
a  sensitive  bromide  plate  covered  with  a  plate 
of  vulcanised  fibre.  An  exposure  of  five  or  ten 
minutes  is  sufficient  to  give  a  good  picture  of  the 
bones,  as  will  be  seen  from  the  frontispiece. 


MINOR  USES  OF   ELECTRICITY.  173 

The  term  "  shadow "  photograph  requires  a 
word  of  explanation.  The  bones  do  not  appear 
as  flat  shadows,  but  rounded  like  solid  bodies,  as 
though  the  active  rays  passed  through  their  sub- 
stance. According  to  Rontgen,  these  "  x  "  rays, 
as  he  calls  them,  are  not  true  cathode  rays,  partly 
because  they  are  not  deflected  by  a  magnet,  but 
cathode  rays  transformed  by  the  glass  of  the 
tube ;  and  they  are  probably  not  ultra-violet 
rays,  because  they  are  not  refracted  by  water  or 
reflected  from  surfaces.  He  thinks  they  are  the 
missing  "  longitudinal  "  rays  of  light  whose  ex- 
istence has  been  conjectured  by  Lord  Kelvin  and 
others — that  is  to  say,  waves  in  which  the  ether 
sways  to  and  fro  along  the  direction  of  the  ray, 
as  in  the  case  of  sound  vibrations,  and  not  from 
side  to  side  across  it  as  in  ordinary  light. 

Be  this  as  it  may,  his  discovery  has  opened 
up  a  new  field  of  research  and  invention.  It  has 
been  found  that  the  immediate  source  of  the  rays 
is  the  fluorescence  and  phosphorescence  of  the 
glass,  and  they  are  more  effective  when  the  fluor- 
escence is  greenish-yellow  or  canary  colour.  Cer- 
tain salts — for  example,  the  sulphates  of  zinc  and 
of  calcium,  barium  platino-cyanide,  tungstate  of 
calcium,  and  the  double  sulphate  of  uranyle  and 
potassium — are  more  active  than  glass,  and  even 
emit  the  rays  after  exposure  to  ordinary  light,  if 
not  also  in  the  dark.  Salvioni  of  Perugia  has 
invented  a  "  cryptoscope,"  which  enables  us  to 
see  the  hidden  object  without  the  aid  of  photog- 
raphy by  allowing  the  rays  to  fall  on  a  plate 
coated  with  one  of  these  phosphorescent  sub- 
stances. Already  the  new  method  has  been 
applied  by  doctors  in  examining  malformations 
and  diseases  of  the  bones  or  internal  organs,  and 


174  THE  STORY  OF  ELECTRICITY. 

in  localising  and  extracting  bullets,  needles,  or 
other  foreign  matters  in  the  body.  There  is  little 
doubt  that  it  will  be  very  useful  as  an  adjunct  to 
hospitals,  especially  in  warfare,  and,  if  the  appa- 
ratus can  be  reduced  in  size,  it  will  be  employed 
by  ordinary  practitioners.  It  has  also  been  used 
to  photograph  the  skeleton  of  a  mummy,  and  to 
detect  true  from  artificial  gems.  However,  one 
cannot  now  easily  predict  its  future  value,  and 
applications  will  be  found  out  one  after  another 
as  time  goes  on. 


CHAPTER  X. 

THE    WIRELESS    TELEGRAPH. 

MAGNETIC  waves  generated  in  the  ether  (see 
pp.  53-95)  by  an  electric  current  flowing  in  a 
conductor  are  not  the  only  waves  which  can  be 
set  up  in  it  by  aid  of  electricity.  A  merely  station- 
ary or  "  static  "  charge  of  electricity  on  a  body, 
say  a  brass  ball,  can  also  disturb  the  ether ;  and  if 
the  strength  of  the  charge  is  varied,  ether  oscilla- 
tions or  waves  are  excited.  A  simple  way  of  pro- 
ducing these  "  electric  waves  "  in  the  ether  is  to 
vary  the  strength  of  charge  by  drawing  sparks 
from  the  charged  body.  Of  course  this  can  be 
done  according  to  the  Morse  code;  and  as  the 
waves  after  travelling  through  the  ether  with  the 
speed  of  light  are  capable  of  influencing  conduc- 
tors at  a  distance,  it  is  easy  to  see  that  signals 
can  be  sent  in  this  way.  The  first  to  do  so  in  a 
practical  manner  was  Signer  Marconi,  a  young 
Italian  hitherto  unknown  to  fame.  In  carrying 


THE   WIRELESS  TELEGRAPH.  175 

out  his  invention,  Marconi  made  use  of  facts  well 
known  to  theoretical  electricians,  one  of  whom, 
Dr.  Oliver  J.  Lodge,  had  even  sent  signals  with 
them  in  1894;  but  it  often  happens  in  science  as 
in  literature  that  the  recognised  professors,  the 
men  who  seem  to  have  everything  in  their  favour 
— knowledge,  even  talent — the  men  whom  most 
people  would  expect  to  give  us  an  original  dis- 
covery or  invention,  are  beaten  by  an  outsider 
whom  nobody  heard  of,  who  had  neither  learn- 
ing, leisure,  nor  apparatus,  but  what  he  could  pick 
up  for  himself. 

Marconi  produces  his  waves  in  the  ether  by 
electric  sparks  passing  between  four  brass  balls, 
a  device  of  Professor  Righi,  following  the  classical 
experiments  of  Heinrich  Hertz.  The  balls  are 
electrified  by  connecting  them  to  the  well-known 
instrument  called  an  induction  coil,  sometimes 
used  by  physicians  to  administer  gentle  shocks  to 
invalids  ;  and  as  the  working  of  the  coil  is  started 
and  stopped  by  an  ordinary  telegraph  key  for  in- 
terrupting the  electric  current,  the  sparking  can 
be  controlled  according  to  the  Morse  code.  In 
our  diagram,  which  explains  the  apparatus,  the 
four  balls  are  seen  at  D,  the  inner  and  larger  pair 
being  partly  immersed  in  vaseline  oil,  the  outer 
and  smaller  pair  being  connected  to  the  secondary 
or  induced  circuit  of  the  induction  coil  C,  which 
is  represented  by  a  wavy  line.  The  primary  or 
inducing  circuit  of  the  coil  is  connected  to  a 
battery  B  through  a  telegraph  signalling  key  K, 
so  that  when  this  key  is  opened  and  closed  by 
the  telegraphist  according  to  the  Morse  code,  the 
induction  coil  is  excited  for  a  longer  or  shorter 
time  by  the  current  from  the  battery,  in  agree- 
ment with  the  longer  and  shorter  signals  of  the 


176  THE  STORY  OF  ELECTRICITY. 

message.  At  the  same  time  longer  or  shorter 
series  of  sparks  corresponding  to  these  signals 
pass  across  the  gaps  between  the  four  balls,  and 
give  rise  to  longer  or  shorter  series  of  etheric 
waves  represented  by  the  dotted  line.  So  much 
for  the  "Transmitter."  But  how  does  Marconi 
transform  these  invisible  waves  into  visible  or 
audible  signals  at  the  distant  place  ?  He  does 
this  by  virtue  of  a  property  discovered  by  Mr.  S. 
A.  Varley  as  far  back  as  1866,  and  investigated  by 
Mr.  E.  Branly  in  1889.  They  found  that  powder 
of  metals,  carbon,  and  other  conductors,  while 
offering  a  great  resistance  to  the  passage  of  an 
electric  current  when  in  a  loose  state,  coheres  to- 
gether when  electric  waves  act  upon  it,  and  op- 
poses much  less  resistance  to  the  electric  current. 
It  follows  that  if  a  Morse  telegraph  instrument  at 
the  distant  place  be  connected  in  circuit  with  a 
battery  and  some  loose  metal  dust,  it  can  be 
adjusted  to  work  when  the  etheric  waves  pass 
through  the  dust,  and  only  then.  In  the  diagram 
R  is  this  Morse  "  Receiver  "  joined  in  circuit  with 
a  battery  B1 ;  and  a  {hin  layer  of  nickel  and  silver 
dust,  mixed  with  a  trace  of  mercury,  is  placed  be- 
tween two  cylindrical  knobs  or  "electrodes"  of 
silver  fused  into  the  glass  tube  */,  which  is  ex- 
hausted of  air  like  an  electric  glow  lamp.  Now, 
when  the  etheric  waves  proceeding  from  the,  trans- 
mitting station  traverse  the  glass  of  the  tube  and 
act  upon  the  metal  dust,  the  current  of  the  battery 
B1  works  the  Morse  receiver,  and  marks  the  sig- 
nals in  ink  on  a  strip  of  travelling  paper.  Inas- 
much as  the  dust  tends  to  stick  together  after  a 
wave  passes  through  it,  however,  it  requires  to  be 
shaken  loose  after  each  signal,  and  this  is  done  by 
a  small  round  hammer  head  seen  on  the  right, 


THE  WIRELESS  TELEGRAPH. 


177 


which  gives  a  slight  tap  to  the  tube.  The  ham- 
mer is  worked  by  a  small  electromagnet  E,  con- 
nected to  the  Morse  instrument,  and  another 
battery  b  in  what  is  called  a  "  relay "  circuit ; 


\AAA/WVWt 


STATION  r.'CElVING  STATION 

FlG.  102.— Marconi's  Apparatus. 

so  that  after  the  Morse  instrument  marks  a  sig- 
nal, the  hammer  makes  a  tap  on  the  tube.  As 
this  tap  has  a  bell-like  sound,  the  telegraphist  can 
also  read  the  signals  of  the  message  by  his  ear. 

Two  "  self-induction  bobbins,"  L  L1,  a  well- 
known  device  of  electricians  for  opposing  resist- 
ance to  electric  waves,  are  included  in  the  circuit 
of  the  Morse  instrument  the  better  to  confine  the 
action  of  the  waves  to  the  powder  in  the  tube. 
Further,  the  tube  d  is  connected  to  two  metal 
conductors  V  V1,  which  may  be  compared  to  reso- 
nators in  music.  They  can  be  adjusted  or  attuned 
to  the  electric  waves  as  a  string  or  pipe  is  to 
sonorous  waves.  In  this  way  the  receiver  can  be 
made  to  work  only  when  electric  waves  of  a  cer- 
tain rate  are  passing  through  the  tube,  just  as  a 
tuning-fork  resounds  to  a  certain  note;  it  being 


1 78  THE  STORY  OF  ELECTRICITY. 

understood  that  the  length  of  the  waves  can 
be  regulated  by  adjusting  the  balls  of  the  trans- 
mitter. As  the  etheric  waves  produced  by  the 
sparks,  like  ripples  of  water  caused  by  dropping 
a  stone  into  a  pool,  travel  in  all  directions  from 
the  balls,  a  single  transmitter  can  work  a  number 
of  receivers  at  different  stations,  provided  these 
are  "  tuned  "  by  adjusting  the  conductors  V  V1  to 
the  length  of  the  waves.  It  is,  therefore,  pos- 
sible to  transmit  secret  messages  by  concealing 
the  nature  of  the  tuning  adjustment,  which  is 
quite  delicate.  Marconi  has  succeeded  in  send- 
ing telegrams  through  the  air  in  this  way  for  from 
twelve  to  fifty  miles.  Changes  of  the  weather, 
such  as  rain,  fog,  wind,  and  snow,  do  not  affect 
the  operation.  It  is  possible,  however,  that  thun- 
derstorms may  sometimes  disturb  the  action,  be- 
cause lightning  flashes  may  give  rise  to  electric 
waves  in  the  ether.  In  order  to  prevent  inter- 
vening hills,  houses,  and  other  objects  from  stop- 
ping the  signals,  the  apparatus  can  be  raised  on 
masts,  or  connected  with  exposed  conductors,  so 
as  to  clear  the  obstacle. 

It  is  obvious  that  the  new  wireless  telegraph 
will  be  useful  in  communicating  between  ship  and 
ship  at  sea  or  ship  and  shore,  or  lighthouse  and 
coastguard.  It  is  likely  to  prove  serviceable  as  a 
fog-signal  and  prevent  collisions  at  sea,  if  not  on 
land.  It  will  enable  trains,  balloons,  and  other 
vehicles  to  send  messages  as  they  go.  Moreover, 
it  will  permit  soldiers  in  the  field  to  keep  in  touch 
with  each  other,  and  outlying  folk  on  islands  and 
mountains  with  the  rest  of  the  world. 


LIST   OF   BOOKS. 


Thomson's  Elementary  Lessons  in  Electricity  and  Magnetism. 

Macmillan. 
Thomson's  Translation  of  Guillemin's  Electricity  and  Mag- 

netism.     Macmillan. 
Foster  and  Atkinson's  Adaptation   of  Joubert's  Elementary 

Treatise  on  Electricity  and  Magnetism.     Longmans. 
Mendenhall's  Century  of  Electricity.     Macmillan. 
Jamieson's  Elementary  Manual  of  Electricity  and  Magnetism. 

Griffin. 

Burch's  Manual  of  Electric  Science.     Methuen. 
Bottone's  Electricity  and  Magnetism.     Whittaker. 
Stewart's  Text-book  of  Magnetism  and  Electricity.     Clive. 
Pope  and  Brackett's  Electricity  in  Daily  Life.     Kegan  Paul. 
Trevert's  Electricity  and  its  Recent  Applications.    Alabaster  & 

Gatehouse. 
Trevert's  Everybody's  Handbook  of  Electricity.     Alabaster  & 

Gatehouse. 

Electrical  Apparatus  for  Amateurs.     Ward  &  Lock. 
Gillett's  Phonograph,  and  How  to  Construct  it.     Spon. 
Ayrton's  Practical  Electricity.     Cassells. 
Fleming's  Short  Lectures  to  Electrical  Artisans.     Spon. 
Slingo  and  Brooker's  Electrical  Engineering.     Longmans. 
Preece  and  Sievewright's  Telegraphy.     Longmans. 
Preece  and  Stubbs'  Manual  of  Telephony.     Whittaker. 
Poole's  Practical  Telephone  Handbook.     Whittaker. 
Bottone's  Dynamo  :    How  Made  and  How  Used.     Sonnen- 

schein. 

Bottone's  Electro-motors  :  How  Made  and  How  Used.    Whit- 
taker. 

Wallis  and  Hawkin's  Dynamos.     Whittaker. 
Allsop's  Induction  Coils.     Spon. 
Allsop's  Practical  Electric  Lighting.     Whittaker. 
Bax's  Popular  Electric  Lighting.     Biggs. 
179 


180  LIST  OP  BOOKS. 

Bottone's  Guide  to  Electric  Lighting  for  Householders.  Whit- 
taker. 

Gordon's  Decorative  Electricity.     Low. 

Reckenzaum's  Electric  Traction.     Biggs. 

Gore's  Electro-Chemistry.     Electrician  Co. 

Benjamin's  Voltaic  Cell.     Wiley,  of  New  York. 

Niblett's  Secondary  Batteries.     Biggs. 

Sloane's  Standard  Electrical  Dictionary.     Lockwood. 

Haycock's  Practical  Electrical  Notes  and  Definitions.     Spon. 

Trevert's  Electrical  Measurements  for  Amateurs.  Alabaster 
&  Gatehouse. 

Southam's  Electrical  Engineering  as  a  Profession.  Whit- 
taker. 

Field's  Story  of  the  Atlantic  Cable.     Gay  &  Bird. 


APPENDIX. 


UNITS  OF   MEASUREMENT. 

(From  Munro  and  Jamiesons  Pocket-book  of  Elec- 
trical Rules  and  Tables). 

I.  FUNDAMENTAL     UNITS.  —  The    electrical 
units  are  derived  from  the  following  mechanical 
units : — 

The  Centimetre  as  a  unit  of  length  ; 
The  Gramme  as  a  unit  of  mass  ; 
The  Second  as  a  unit  of  time. 
The    Centimetre   is    equal    to    0.3937    inch   in 
length,  and  nominally  represents  one  thousand- 
millionth  part,  or  looo^Tnr.innr  °f  a  quadrant  of 
the  earth. 

The  Gramme  is  equal  to  15.432  grains,  and 
represents  the  mass  of  a  cubic  centimetre  of  wa- 
ter at  4°  C.  Mass  is  the  quantity  of  matter  in 
a  body. 

The  Second  is  the  time  of  one  swing  of  a  pen- 
dulum making  86,164.09  swings  in  a  sidereal  day, 
or  -^-,£75-5-  part  of  a  mean  solar  day. 

II.  DERIVED  MECHANICAL  UNITS. — 

Area. — The  unit  of  area  is  the  square  centi- 
metre. 

iSi 


1 82  APPENDIX. 

Volume. — The  unit  of  volume  is  the  cubic  centi- 
metre. 

Velocity  is  rate  of  -change  of  position.  It  in- 
volves the  idea  of  direction  as  well  as  that  of 
magnitude.  Velocity  is  uniform  when  equal  spaces 
are  traversed  in  equal  intervals  of  time.  The 
unit  of  velocity  is  the  velocity  of  a  body  which 
moves  through  unit  distance  in  unit  time,  or  the 
velocity  of  one  centimetre  per  second. 

Momentum  is  the  quantity  of  motion  irT  a  body, 
and  is  measured  by  mass  x  velocity. 

Acceleration  is  the  rate  of  change  of  velocity, 
whether  that  change  take  place  in  the  direction 
of  motion  or  not.  The  unit  of  acceleration  is 
the  acceleration  of  a  body  which  undergoes  unit 
change  of  velocity  in  unit  time,  or  an  acceleration 
of  one  centimetre-per-second  per  second.  The 
acceleration  due  to  gravity  is  considerably  greater 
than  this,  for  the  velocity  imparted  by  gravity  to 
falling  bodies  in  one  second  is  about  981  centi- 
metres per  second  (or  about  32.2  feet  per  second). 
The  value  differs  slightly  in  different  latitudes. 
At  Greenwich  the  value  of  the  acceleration  due  to 
gravity  is  g  =  981.17  ;  at  the  Equator  g  =  978.1 ; 
at  the  North  Pole  g  =  983.1. 

Force  is  that  which  tends  to  alter  a  body's 
natural  state  of  rest  or  of  uniform  motion  in  a 
straight  line. 

Force  is  measured  by  the  acceleration  which 
it  imparts  to  mass  —  i.  e.,  mass  X  accelera- 
tion. 

The  Unit  of  Force,  or  Dyne,  is  that  force  which, 
acting  for  one  second  on  a  mass  of  one  gramme, 
gives  to  it  a  velocity  of  one  centimetre  per 
second.  The  force  with  which  the  earth  attracts 
any  mass  is  usually  called  the  "weight-"  of  that 


APPENDIX.  183 

mass,  and  its  value  obviously  differs  at  different 
points  of  the  earth's  surface.  The  force  with 
which  a  body  gravitates  —  i.e.,  its  weight  (in 
dynes),  is  found  by  multiplying  its  mass  (in 
grammes)  by  the  value  of  g  at  the  particular 
place  where  the  force  is  exerted. 

Work  is  the  product  of  a  force  and  a  distance 
through  which  it  acts.  The  unit  of  work  is  the 
work  done  in  overcoming  unit  force  through 
unit  distance  —  /.  £.,  in  pushing  a  body  through  a 
distance  of  one  centimetre  against  a  forch  of  one 
dyne.  It  is  called  the  Erg.  Since  the  "  weight  " 
of  one  gramme  is  i  X  981  or  981  dynes,  the  work 
of  raising  one  gramme  through  the  height  of  one 
centimetre  against  the  force  of  gravity  is  981 
ergs  or  g  ergs.  One  kilogramme-metre  =  100,000 
(g)  ergs  =  9.81  X  io7  ergs.  One  foot-pound  = 
I3»825  Or)  er£s>  —  J-356  X  io7  ergs. 

Energy  is  that  property  which,  possessed  by  a  body,  gives 
it  the  capability  of  doing  work.  Kinetic  energy  is  the  work  a 
body  can  do  in  virtue  of  its  motion.  Potential  energy  is  the 
work  a  body  can  do  in  virtue  of  its  position.  The  unit  of 
energy  is  the  Erg. 

Power  or  Activity  is  the  rate  of  work  ;  the  prac- 
tical unit  is  called  the  Watt  =.  io7  ergs  per  second. 

A  Horse-power  =  33,000  ft.-lbs.  per  minute  = 

550  ft.-lbs.  per  second  ;  but  as  seen  above  under 

Work,   i   ft.-lb.  =    1.356  X  io7  ergs,   and    under 

Power  ',  i    Watt  =  io7  ergs  per  sec.  .*.   a  Horse- 

power =  550  X  1.356  X  io7  ergs  =  746  Watts; 


or,  =          =  _         =  H.P. 

746        746        746  R 
where  E  =  volts,  C  =  amperes,  and  R  =  ohms. 

The  French  "force  de  cheval"  =  75  kilogramme 
metres  per  sec.  =  736  Watts  —  542.48  ft.-lbs.  per 


1 84  APPENDIX. 

sec.  =  -9863  H.P. ;  or  one  H.P.  =  1.01385  "force 
de  cheval." 

Derived  Electrical  Units — There  are  two  sys- 
tems of  electrical  units  derived  from  the  funda- 
mental "C.G.S."  units,  one  set  being  based  upon 
the  force  exerted  between  two  quantities  of  elec- 
tricity, and  the  other  upon  the  force  exerted  be- 
tween two  magnetic  poles.  The  former  set  are 
termed  electro- static  units,  the  latter  electro-magnetic 
units. 

III.  ELECTROSTATIC  UNITS. — 

Unit  quantity  of  electricity  is  that  which  repels 
an  equal  and  similar  quantity  at  unit  distance 
with  unit  force  in  air. 

Unit  current  is  that  which  conveys  unit  quan- 
tity of  electricity  along  a  conductor  in  a  second. 

Unit  electromotive  force,  or  unit  difference  of 
potential  exists  between  two  points  when  the  unit 
quantity  of  electricity  in  passing  from  one  to  the 
other  will  do  the  unit  amount  of  work. 

Unit  resistance 'is  that  of  a  conductor  through 
which  unit  electromotive  force  between  its  ends 
can  send  a  unit  current. 

Unit  capacity  is  that  of  a  condenser  which  con- 
tains unit  quantity  when  charged  to  unit  differ- 
ence of  potential. 

IV.  MAGNETIC  UNITS. — 

Unit  magnetic  pole  is  that  which  repels  an  equal 
and  similar  pole  at  unit  distance  with  unit  force 
in  air. 

Strength  of  Magnetic  Field  at  any  point  is 
measured  by  the  force  which  would  act  on  a  unit 
magnetic  pole  placed  at  that  point. 


APPENDIX.  185 

Unit  Intensity  of  Field  is  that  intensity  of  field 
which  acts  on  a  unit  pole  with  unit  force. 

Moment  of  a  Magnet  is  the  strength  of  either 
pole  multiplied  by  the  distance  between  the  poles. 

Intensity  of  Magnetisation  is  the  magnetic  mo- 
ment of  a  magnet  divided  by  its  volume. 

Magnetic  Potential. — The  potential  at  a  point 
due  to  a  magnet  is  the  work  that  must  be  done  in 
removing  a  unit  pole  from  that  point  to  an  in- 
finite distance  against  the  magnetic  attraction,  or 
in  bringing  up  a  unit  pole  from  an  infinite  dis- 
tance to  that  point  against  the  magnetic  repul- 
sion. 

Unit  Difference  of  Magnetic  Potential. — Unit 
difference  of  magnetic  potential  exists  between 
two  points  when  it  requires  the  expenditure  of 
one  erg  of  work  to  bring  an  (N.  or  S.)  unit  mag- 
netic pole  from  one  point  to  the  other  against  the 
magnetic  forces. 

V.  ELECTRO-MAGNETIC  UNITS. — 

Unit  current  is  that  which  in  a  wire  of  unit 
length,  bent  so  as  to  form  an  arc  of  a  circle  of 
unit  radius,  would  act  upon  a  unit  pole  at  the 
centre  of  the  circle  with  unit  force. 

Unit  quantity  of  electricity  is  that  which  a  unit 
current  conveys  in  unit  time. 

Unit  electro-motive  force  or  difference  of  potential 
is  that  which  is  produced  in  a  conductor  moving 
through  a  magnetic  field  at  such  a  rate  as  to  cut 
one  unit  line  per  second. 

Unit  resistance  is  that  of  a  conductor  in  which 
unit  current  is  produced  by  unit  electro-motive 
force  between  its  ends. 

Unit  capacity  is  that  of  a  condenser  which  will 


1 86  APPENDIX. 

be  at  unit  difference  of  potential  when  charged 
with  unit  quantity. 

Electric  and  magnetic  force  varies  inversely  as  the  square 
of  the  distance. 


PRACTICAL   UNITS   OF   ELECTRICITY. 

RESISTANCE — R. — The  Ohm  is  the  resistance 
of  a  column  of  mercury  106.3  centimetres  long, 
i    square   millimetre   in    cross-section,   weighing 
14.4521    grammes,   and   at  a  temperature   of   o° 
centigrade.     Standards  of  wire  are  used  for  prac- 
tical  purposes.      The   ohm  is   equal   to  a  thou- 
sand million,  io9,  electromagnetic  or  Centimetre- 
Gramme-Second  ("  C.  G.  S.")  units  of  resistance. 
The  megohm  is  one  million  ohms. 
The  microhm  is  one  millionth  of  an  ohm. 
ELECTROMOTIVE  FORCE — E. — The  Volt  is  that 
electromotive  force  which  maintains  a  current  of 
one  ampere  in  a  conductor  having  a  resistance  of 
one  ohm.     The  electromotive  force  of  a  Clark 
standard  cell  at  a  temperature  of  15°  centigrade 
is   1.434  volts.     The  volt  is  equal  to  a  hundred 
million,  io8,  C.  G.  S.  units  of  electromotive  force. 
CURRENT — C. — The  Ampere  is  that  current  which 
will  decompose  0.09324  milligramme  of  water 
(H2O)    per    second   or   deposit    1.118    milli- 
grammes of  silver  per  second.     It  is  equal  to 
one-tenth  of  a  C.  G.  S.  unit  of  current. 
The  milliampere  is  one  thousandth  of  an  ampere. 
QUANTITY — Q. — The  Coulomb  is  the  quantity  of 
electricity  conveyed  by  an  ampere  in  a  sec- 
ond.    It  is  equal  to  one-tenth  of  a  C.  G.  S. 
unit  of  quantity. 

The  micro-coulomb  is  one  millionth  of  a  coulomb. 
CAPACITY — K. — The  Farad  is  that  capacity  of  a 


APPENDIX.  187 

body,  say  a  Leyden  jar  or  condenser,  which 
a  coulomb  of  electricity  will  charge  to  the 
potential  of  a  volt.  It  is  equal  to  one  thou- 
sand-millionth of  a  C.  G.  S.  unit  of  capacity. 

The  micro-farad  is  one  millionth  of  a  Farad. 

By  Ohm's  Law,  Current  =  Electromotive  Force  -f- 
Resistance, 

orC=| 

Volt 


Hence  when  we  know  any  two  of  these  quan- 
tities, we  can  find  the  third.  For  example,  if 
we  know  the  electromotive  force  or  differ- 
ence of  potential  in  volts  and  the  resistance 
in  ohms  of  an  electric  circuit,  we  can  easily 
find  the  current  in  amperes. 

POWER  —  P.  —  The  Watt  is  the  power  conveyed  by 
a  current  of  one  ampere  through  a  conductor 
whose  ends  differ  in  potential  by  one  volt,  or, 
in  other  words,  the  rate  of  doing  work  when 
an  ampere  passes  through  an  ohm.  It  is 
equal  to  ten  million,  io7,  C.  G.  S.  units  of 
power  or  ergs  per  second,  that  is  to  say,  to  a 
Joule 

per  second,  or  _L.  of  a  horse-power. 
746 

A  Watt  =  volt  X  ampere,  and  a  Horse-power  = 
Watts  -f-  746. 

HEAT  OR  WORK  —  W.  —  The/^/*  is  the  work  done 
or  heat  generated  by  a  Watt  in  a  second,  that 
is,  the  work  done  or  heat  generated  in  a  sec- 
ond by  an  ampere  flowing  through  the  resist- 
ance of  an  ohm.  It  is  equal  to  ten  million, 
io7,  C.  G.  S.  units  of  work  or  ergs.  Assum- 


1 88  APPENDIX. 

ing  "Joule's  equivalent"  of  heat  and  me- 
chanical energy  to  be  41,600,000,  it  is  the 
heat  required  to  raise  .24  gramme  of  water  i° 
centigrade.  A  Joule  =  Volt  X  ampere  X  sec- 
ond. Since  i  horse-power  =  550  foot  pounds 
of  work  per  second, 

W  =  55?E.Q.  =  .7373  E.Q.  foot  pounds. 
746 

HEAT  UNITS. 

The  British  Unit  is  the  amount  of  heat  required 
to  raise  one  pound  of  water  from  60°  to  61° 
Fahrenheit.  It  is  251.9  times  greater  than 
the  metric  unit,  therm  or  calorie,  which  is  the 
amount  of  heat  required  to  raise  one  gramme 
of  water  from  4°  to  5°  centigrade. 

Joule's  Equivalent — J. — is  the  amount  of  energy 
equivalent  to  a  therm  or  calorie,  the  metric 
unit  of  heat.  It  is  equal  to  41,600,000  ergs. 

The  heat  in  therms  generated  in  a  wire  by  a 
current  =  Volt  X  ampere  X  time  in  seconds 
X  0.24. 

LIGHT  UNITS 

The  British  Unit  is  the  light  of  a  spermaceti 
candle  7/8-inch  in  diameter,  burning  120  grains 
per  hour  (six  candles  to  the  pound).  They 
sometimes  vary  as  much  as  10  per  cent,  from 
the  standard.  Mr.  Vernon  Harcourt's  stand- 
ard flame  is  equal  to  an  average  standard 
candle. 

The  French  Unit  is  the  light  of  a  Carcel  lamp, 
and  is  equivalent  to  9J/2  British  units. 


INDEX. 


A. 

Dynamos,  magneto-electric,  67. 
reversibility  of,  65,  73. 

Amber,  9. 

series,  70. 

Ampere,  76,  186. 

shunt,  71. 

Accumulator,  39. 

E.  P.  S.,  40- 

E. 

Faure,  39. 

Grove  gas,  39. 

Electric  alarms,  146. 

Plante,  39. 

burglar,  148. 

Sellon-Volckmar,  40. 

fire,  147. 

Appendix,  181. 

frost,  149. 

Arc,  electric,  no,  122. 

torpedo,  149. 

water,  149. 

B. 

Electric  arc,  no. 

arc  lamps,  in. 

Books,  list  of,  179. 

bell,  143. 

boat,  128. 

C. 

carriage,  128. 

chronograph,  151. 

Capacity,  186. 

circuits,  118. 

Coal,  electricity  from,  131. 
Code,  Morse  telegraph,  87,  101. 

city,  132. 
clocks,  150. 

Compass,  mariner's,  46. 

compass,  150. 

Condenser,  62. 

cooking,  123. 

Conduction,  16. 

cut-outs,  120. 

Conductors,  16. 

divining  rod,  155. 

Coulomb,  76,  186. 
Current,  electric,  57. 

drill,  133. 
fishes,  163. 

electromotive  force  of,  74. 
attraction  of,  57. 

forces,  n. 
furnace,  122. 

Ohm's  law  for,  76. 
potential  of,  75. 

fuse,  163. 
gaslighter,  160. 

pressure  of,  74. 
Currents,  electric,  resistance  of,  74, 

heat,  122. 
incandescent  lamps,  123. 

75- 

induction  glows,  120. 

rules  for  direction  of,  56,  65,  66. 

light  signals,  152. 

lamp-lighter,  162. 

D. 

log,  149. 

meters,  152. 

Diamagnetism,  51. 

motor,  73. 

Dynamos,  67. 

pen,  156. 

compound,  73. 
Gramme,  69. 

power,  124. 
power,  transmission  of,  135. 

189 


190 


INDEX. 


Electric  quilt,  124. 

Induction  coil,  61. 

radiator,  124. 
railway,  126. 

magneto  electric,  154. 
magneto,  direction  of  current,  56, 

search  light,  153. 

66. 

sewing  machine,  132. 

Inductive  capacity,  20. 

shock,  treatment  for,  163. 

Insulation,  16. 

silhouettes,  167. 

Insulators,  16. 

torpedo,  130. 

Ion,  76. 

tramway,  126. 

tricycle,  128. 

ventilator,  130. 

• 

weather  'vane,  150. 

Joule,  187. 

welding,  122. 
Electricity,  chemistry  and,  26. 
coal  and,  131. 
friction  and,  9. 

Joule's  equivalent,  188. 
L. 

heat  and,  41. 

Ley  den  jar,  21. 

magnetism  and,  45. 

Light,  unitt  188. 

Niagara  and,  132. 
origin  of  the  science,  10. 

Lightning,  nature  of,  25. 
rods,  25. 

peat  and,  131. 
scale  of  bodies  producing,  14. 

rod  testing,  164. 
shock,  treatment  for,  163. 

surface,  17. 

Lodestone,  46. 

Electro-cautery,  162. 
Electro-chemical  equivalent,  77. 
Electro  chemistry,  26. 
Electro-deposition  of  metals,  77. 

M. 

Magnet,  horse-shoe,  54. 

Electrolysis,  74. 

natural,  47. 

Electromagnetism,  59. 
Electromagnet,  60. 
Electromedicine,  163. 

Magnetic  compass,  origin  of,  46. 
Magnetic  lines  of  force,  54,  57. 
Magnetism,  45. 

Electromotive  force,  29,  74. 
Electrophorus,  20. 

connection  with  electricity,  55, 
earth's,  49. 

Electroplating,  78. 

earth's,  forces  of,  50. 

Electrotyping,  80. 

earth's,  theory  of,  52. 

Energy,  183. 

Magnetite,  46. 

Measurement,  units  of,  181. 

F. 

Microphone,  Hughes',  104. 

Morse  code,  87. 

Farad,  186. 

telegraph,  88. 

Motor,  electric,  73. 

G. 

Galvanism,  discovery  of,  26. 

N. 

Galvanometer,  56. 

Niagara,  electricity  from,  1320 

Galvanoscope,  56. 
Geissler  tubes,  63,  168. 

0. 

H. 

Ohm.  76,  186. 

Ohm  s  law,  76,  187. 

Heat,  41,  188. 

unit,  184. 

p^ 

Hysteresis,  magnetic,  53, 

Paramagnetism,  51. 

I. 

Peat,  electricity  from,  131, 

Peltier  effect,  45. 

Induction,  18. 

Phonograph,  156. 

balance,  154. 

Photo-electric  cell,  154. 

INDEX. 


J9I 


Photophone,  153. 

Telephone,  Bell,  102. 

cable,  107. 

Pressure  of  a  current,  74. 

Chicago  to  New  York,  107. 

Primary  cells,  37. 
coils,  61. 
current,  61. 

Edison,  103. 
exchange,  107. 
instrument  of  Blake,  107. 
switchboard^  108. 

R. 

Thermo-electricity,  41. 
Thermo-electric  couple,  41. 

Resistance,  30. 

in  series,  43. 
piles,  44. 

S. 

scale,  42. 

Secondary  cells,  37. 

U. 

coils,  61. 
currents,  61. 

Units,  181. 

Shocks,  electric,  163. 

Sonometer,  155. 

V. 

Sounder,  90. 
Storage  cell,  37. 
Submarine  cable,  95 
Atlantic,  96. 

Volt,  76,  186. 
Voltaic  cell,  27. 
action  of,  28. 
bichromate,  28. 

mirror  instrument,  99. 
signal  alphabet,  101. 
siphon  recorder,  100. 
speed  of  messages,  zoz. 

Bunsen,  33. 
Chloride  of  silver,  35. 
Clark  Standard,  36. 
Coupling,  31. 
Dn 

detector,  155. 

aniell,  32. 
Dry  "  E.  C.  C.,"  36. 

T. 

Hellesen,  37. 
Leclanche-Barbier,  37. 

Telautograph,  93.  ^ 
Telegrams,  errors  in,  92. 
Telegraph,  automatic  sender,  91. 
chemical,  90. 
circuit,  84. 

Grove,  33. 
Grove  gas,  39. 
Leclanche,  34. 
Schanschieff,  36. 
Skrivanoff,  36. 

C.  M.'s,  24. 
Cooke  and  Wheatstone,  82. 
domestic,  150. 

Smee,  33. 
Voltaic  electricity,  discovery  of,  27^ 
Voltameter,  38. 

duplex  system,  92. 

Hughes,  91. 
Kelvin,  99. 

W. 

Morse,  88. 

Water,  decomposition  of,  37. 

origin  of,  81. 

Watt,  187. 

Ronald's,  24. 
Vail,  90. 

Wheatstone  bridge,  164. 
Wireless  telegraph,  174. 

wireless,  174.                                       I  Work,  183,  187. 

(10) 


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